A U G U S T 2 0 2 1

INVESTOR PRESENTATION

DISCLAIMERSForward‐Looking Statements

This presentation contains comments or information that constitute forward-looking statements (within the meaning of the Private Securities Litigation Reform Act of 1995), which involve significant risks and uncertainties. Forward-looking statements often use words such as “anticipate,” “could,” “target,” “expect,” “estimate,” “intend,” “plan,” “goal,” “forecast,” “believe,” or other words of similar meaning. These statements are based on the current beliefs and expectations of the Company’s management and are subject to significant risks and uncertainties. Actual results may differ materially from the results discussed in the forward-looking statements. Moreover, the Company’s plans, objectives and intentions are subject to change based on various factors (some of which are beyond the Company’s control). Factors that could cause actual results to differ from those discussed in the forward-looking statements include: (1) the macroeconomic and other challenges and uncertainties related to the COVID-19 pandemic, variants of COVID-19, and related vaccine rollout and efficacy, including the negative impacts and disruptions on public health, the Company’s corporate and consumer customers, the communities the Company serves, and the domestic and global economy, which may have an adverse effect on the Company’s business; (2) current and future economic and market conditions, including the effects of a decline in housing or vehicle prices, higher unemployment rates, labor shortages, inability to obtain raw materials and supplies, U.S. fiscal debt, budget and tax matters, geopolitical matters, and any slowdown in global economic growth; (3) changes to the U.S. Small Business Administration (“SBA”) Paycheck Protection Program (the “PPP”), including to the rules under which the PPP is administered, with respect to the origination, servicing, or forgiveness of PPP loans, whether now existing or originated in the future, or the terms and conditions of any guaranteed payments due to the Company from the SBA with respect to PPP loans; (4) the effect of, and changes in, monetary and fiscal policies and laws, including interest rate and other policy actions of the Board of Governors of the Federal Reserve System; (5) the effect of changes in the level of checking or savings account deposits on the Company’s funding costs and net interest margin; (6) future provisions for credit losses on loans and debt securities; (7) changes in nonperforming assets; (8) the effect of a fall in stock market or bond prices on the Company’s fee income businesses, including its employee benefit services, wealth management, and insurance businesses; (9) risks related to credit quality; (10) inflation, interest rate, liquidity, market and monetary fluctuations; (11) the strength of the U.S. economy in general and the strength of the local economies where the Company conducts its business; (12) the timely development of new products and services and customer perception of the overall value thereof (including features, pricing and quality) compared to competing products and services; (13) changes in consumer spending, borrowing and savings habits; (14) technological changes and implementation and financial risks associated with transitioning to new technology-based systems involving large multi-year contracts; (15) the ability of the Company to maintain the security of its financial, accounting, technology, data processing and other operating systems and facilities; (16) effectiveness of the Company’s risk management processes and procedures, reliance on models which may be inaccurate or misinterpreted, the Company’s ability to manage its credit or interest rate risk, the sufficiency of its allowance for credit losses and the accuracy of the assumptions or estimates used in preparing the Company’s financial statements and disclosures; (17) failure of third parties to provide various services that are important to the Company’s operations; (18) any acquisitions or mergers that might be considered or consummated by the Company and the costs and factors associated therewith, including differences in the actual financial results of the acquisition or merger compared to expectations and the realization of anticipated cost savings and revenue enhancements; (19) the ability to maintain and increase market share and control expenses; (20) the nature, timing and effect of changes in banking regulations or other regulatory or legislative requirements affecting the respective businesses of the Company and its subsidiaries, including changes in laws and regulations concerning taxes, accounting, banking, risk management, securities and other aspects of the financial services industry, specifically the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010 or those emanating from COVID-19; (21) changes in the Company’s organization, compensation and benefit plans and in the availability of, and compensation levels for, employees in its geographic markets; (22) the outcome of pending or future litigation and government proceedings; (23) other risk factors outlined in the Company’s filings with the SEC from time to time; and (24) the success of the Company at managing the risks of the foregoing.

Note Regarding Non‐GAAP Financial MeasuresThe Company also provides supplemental reporting of its results on an “operating,” “adjusted” and “tangible” basis, from which it excludes the after-tax effect of amortization of core deposit and other intangible assets (and the related goodwill, core deposit intangible and other intangible asset balances, net of applicable deferred tax amounts), accretion on non-impaired purchased loans, expenses associated with acquisitions and the unrealized gain (loss) on equity securities. Although these items are non-GAAP measures, the Company’s management believes this information helps investors and analysts measure underlying core performance and improves comparability to other organizations that have not engaged in acquisitions. In addition, the Company provides supplemental reporting for “adjusted pre-tax, pre-provision net revenues,” which excludes the provision for credit losses, acquisition expenses and the unrealized gain (loss) on equity securities from income before income taxes. Although adjusted pre-tax, pre-provision net revenue is a non-GAAP measure, the Company’s management believes this information helps investors and analysts measure and compare the Company’s performance through a credit cycle by excluding the volatility in the provision for credit losses associated with the adoption of CECL and the economic uncertainty caused by the COVID-19 pandemic. This presentation includes a reconciliation of each non-GAAP financial measure to the most comparable GAAP equivalent.

2

COMPANY PROFILE

• Successful, growing community bank headquartered outside of Syracuse, New York.

• One of the largest community banks based in Upstate New York with approximately $14.8 billion1 in total assets.

• More than 225 customer banking facilities across Upstate New York, Northeast Pennsylvania, Vermont and Massachusetts.

• Dominant market share: 1st or 2nd in approximately two-thirds of the towns where we do business

• Significant and growing fee based non-banking businesses

• Market capitalization of $3.86 billion (at 7/30/21 share price of $71.64)

(1) As of June 30, 2021(2) Total return based on 10-year historical performance through July 30, 2021 assuming dividend reinvestment.

COMPANY STRENGTHS

• Track record of superior shareholder returns

• Our 10-year cumulative total return to shareholders is 283% (14.4% annualized). This compares to a 10-year cumulative total return for the KBW Regional Banking Index of 192% (11.3% annualized). (2)

• Industry leading dividend record – 29 consecutive years of increases.

• Strong asset quality even through the great recession and COVID-19 Pandemic

• Primarily non-urban footprint provides stable, 2% to 5% growth a year.

• Focus on smaller, in-footprint customers than our large competitors.

• Significant fee based non-banking businesses reduce dependence on net interest income.

• Employee Benefit Services, Wealth Management and Insurance contributed approximately 74% of the Company’s noninterest income in Q2 2021.

3

RECENT ACCOMPLISHMENTS

• Navigated challenges of COVID pandemic, while generating solid operating results in the second quarter of 2021• Return on Assets – 1.31%• Return on Equity – 9.61%• Return on Tangible Equity – 16.0% (1)

• Deposit Funding Costs – 0.10%• GAAP EPS – $0.88; up $0.22 per share from the second quarter of 2020• Operating EPS (2) – $0.88; up $0.12 per share from the second quarter of 2020

• Raised our dividend in July 2021 for the 29th consecutive year, retaining our “Dividend Aristocrat“ Status• In 2021, identified as a “Performance Powerhouse” by Bank Director Magazine. Ranked #1 in retail strategy.• Regularly in the Top 10 of America’s best large banks by Forbes Magazine. Ranked #7 for the 2021 list.• Maintained strong asset quality. Part of our operating DNA

• -0.03% net charge off ratio in Q2 2021.• 0.07% net charge off ratio in 2020

(1) Return on Tangible Equity is calculated by dividing Net Income by Average Shareholders’ Equity less average intangible assets, net of deferred tax on intangible assets.(2) Operating earnings are a non-GAAP measure and exclude one time securities gains, merger related expenses and special charges; net of tax effect. Please see Appendix for

details.

STRATEGIC PROFILE• Consistent business model for over 20 years

• Market-leading branch system serving predominantly non-urban markets

• Excellent core deposit customer base

• Decentralized decision-making and authority

• Investment in noninterest revenue businesses

• Goal of 10% annual total shareholder return over time

• Disciplined growth through organic and acquired opportunities; focused on profitable relationships

• Focused on low risk accretive transactions

4

OPERATING PERFORMANCE SUMMARYQ2 2021

In Millions(except EPS)

% Changefrom Q2 2020

YTD 2021In Millions

(except EPS)

% Changefrom YTD 2020

Net interest income $92.1 0.2% $186.1 2.2%

Noninterest revenues 59.5 12.3% 118.0 5.7%

Operating expenses (1) 93.5 6.9% 186.8 3.3%

Provision for credit losses (4.3) NM (10.1) NM

Net income, operating 47.9 18.5% 100.8 24.5%

Fully diluted weighted average common shares outstanding 54.6 3.0% 54.5 3.2%

GAAP EPS (diluted) $0.88 33.3% $1.85 29.4%

Operating EPS (diluted)(2) $0.88 15.8% $1.85 20.9%

(1) Excludes acquisition expenses and special charges.(2) Operating earnings are a non-GAAP measure and exclude one time securities gains, merger related expenses and special charges; net of tax effect. Please see

Appendix for details.(3) Adjusted pre-tax, pre-provision (“PTPP”) net revenue is a non-GAAP measure. Please see the Appendix for details.

$57.3 $58.0

$1.08 $1.06

$0.80

$0.90

$1.00

$1.10

$1.20

$50$52$54$56$58$60

Q2 2020 Q2 2021

PTPP EPS

PTPP

Net

Rev

enue

, $ in

M

illio

ns

Adjusted pre-tax, pre-provision net revenue

Adjusted PTPP EPS

$112.8

$117.3

$2.13 $2.15

$2.00

$2.10

$2.20

$2.30

$100

$110

$120

YTD 2020 YTD 2021

PTPP EPS

PTPP

Net

Rev

enue

, $ in

M

illio

ns

Adjusted pre-tax, pre-provision net revenue

Adjusted PTPP EPS

ADJUSTED PRE-TAX, PRE-PROVISION (“PTPP”) RESULTS

(3) (3)

5

STRATEGY ELEMENT #1

MARKET-LEADING BRANCH/DIGITAL SERVICE STRATEGY FOCUSED ON CORE ACCOUNTS

• Emphasize responsive, local decision-making and customer service and support, and authority at the branch level

• Focus on generating and retaining core deposit accounts

• Mostly non-urban markets where leadership positions can be earned

• Complement market-leading branch system with enhanced digital banking services, including online deposit account opening and loan applications

Counties with Community Bank Retail Banking Locations

OPERATING AND LENDING STRATEGIES ARE LOCAL AND CONSERVATIVE• Community bank approach to growth

• Discipline and focus on our local customers

• An in-footprint lender with deep knowledge of our markets

• Emphasis on profitable customer relationships across all business lines

• Decentralized local decision-marking – branch managers act as local bank presidents

• Average loan originations are uniquely granular for an institution of our size• Average Residential Mortgage – $128,000

• Average Home Equity – $65,000

• Average Indirect Loan – $21,000

• Average Commercial Loan Relationship of $540,000(1)

• Commercial loan mix is well-diversified

(1) Excludes Paycheck Protection Program (“PPP”) loans

Customer Facing Technology Investments

(“Bring the Branch to the Customer”)

New Mobile Banking app in 2020•Enhanced personal banking budgeting tool•Pursuing enhanced functionality for person to person payments

20% of residential mortgage applications are now submitted online

Developing online small business loan application portal

Enhancing Treasury Management tool for business and municipal customers

Developed and utilized loan application portal for second draw PPP loans

Enhancing E-Sign / Digital Signature capabilities

Additional Technology Investments

Investing resources in Application Development Department

Workflow automation technology

Enhancing card management technology (restrictions & alerting)

Rolled out micro business digital banking platform to assist invoicing, payments and bookkeeping

Continually investing in information security infrastructure across banking and financial services businesses

Shifted marketing budget to drive digital traffic

TECHNOLOGY INVESTMENTS

7

DIGITAL BANKING USAGE & ADOPTION RATES

100,000

125,000

150,000

175,000

200,000

225,000

250,000

Digital Banking Users (active)

45,000 50,000 55,000 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000

Online Bill Pay Users (consumer)

70,000 90,000

110,000 130,000 150,000 170,000 190,000 210,000 230,000 250,000

E-Statement Users

Enrolled Users: 51% of Total Customers(July 2021)

22% of Consumer Core Deposit Customers(July 2021)

51% of Core Deposit Customers(July 2021)

New mobile banking app

8

TRANSACTION TRENDS

3,500

4,000

4,500

5,000

5,500

6,000

6,500

7,000

7,500

400

500

600

700

800

900

1,000

Jan '20 Feb '20 Mar '20 Apr '20 May '20 June '20 Jan '21 Feb '21 Mar '21 Apr '21 May '21 June '21

Debit C

ard Transactions

Thousands

Bran

ch T

rans

actio

ns

Thou

sand

s

Branch Transactions Debit Card Transactions

3

107

3 7

3

13 14

02468

10121416

2019 2020 2021

# of Branches Consolidated Consolidated as part of Steuben Transaction # of Branches to be Consolidated

BRANCH CONSOLIDATIONS

9

STRATEGY ELEMENT #2

(1) Excluding securities gains/losses and debt extinguishment gains/losses

CONTINUE TO FOCUS ON MULTIPLE CHANNELS OF NONINTEREST REVENUES• Banking Services

• $15.5 million in Q2 2021(1) (26% of total)

• Employee Benefit Plan Administration and Trust Services• $27.5 million in Q2 2021 (46% of total)

• Wealth Management & Insurance• $16.4 million in Q2 2021 (28% of total)

$47.0 $58.5 $73.4 $66.4$10.7

$17.9

$48.2 $60.3$31.6

$42.6

$80.8$101.3

$89.3

$119.0

$202.4

$228.0

$0

$60

$120

$180

$240

2011 2014 2017 2020

$ in

Mill

ions

Banking Noninterest Revenues Wealth Management and Insurance Benefit Plan Services

Noninterest Revenues / Operating Revenues = 39% in Q2 2021

(1)

10

EMPLOYEE BENEFIT PLAN ADMINISTRATION & TRUST SERVICES

• Revenue Growth 10-year CAGR 13.1% (2010-2020)

• $101.3 million of revenues in 2020, a 4.3% increase over 2019

• $27.5 million of revenues in Q2 2021, a 14.2% increase over Q2 2020

• National administrator of retirement plans, employee benefit plans, fund of funds, and collective investment trusts

• 4,200 retirement plans, $110 billion in trust assets and more than 510,000 participants

• 10 offices across the U.S. and Puerto Rico and 370 employees

• Breadth of services, depth of creative talent, and financial resources to help clients solve benefit plan challenges without engaging multiple providers

• BPAS Family of ServicesPlan Administration & Recordkeeping | TPA | Actuarial & Pension | VEBA & HRA/HSA | Fiduciary | AutoRollovers & MyPlanLoan | Healthcare Consulting | Transfer Agency | Fund Administration | Collective Investment Funds

• BPAS SubsidiariesHand Benefits & Trust | NRS Trust Product Administration | Global Trust Company | BPAS Trust Company of Puerto Rico

• Specialty Retirement Plan Administration PracticesAuto Enrollment Plans | Multiple Employer Plans and Multiple Employer Trusts| Plans with Employer Securities | Puerto Rico Section 1081 Plans | VEBA HRA Plans | Cash Balance Plans | Collective Investment Funds | Fund Administration

One company. One Call.

11

WEALTH MANAGEMENT AND INSURANCE

• Revenue Growth 10-year CAGR 19.9% (2010-2020)

• $60.3 million of revenues in 2020, a 3.8% increase over 2019

• $16.4 million of revenues in Q2 2021, a 13.0% increase over Q2 2020

• Upstate NY, Northeast PA, Vermont, NYC, and Florida

• $8.8 billion in assets under management or administration‒ Trust Services

‒ Asset Management and Advisory

‒ Insurance Agency

‒ Risk Management Services

‒ Planning

• Wealth Management Subsidiaries• Community Investment Services, Inc. (CISI) – Comprehensive Planning and Investment Services

• Nottingham Advisors – Asset Management Services

• Community Bank Trust Services – Trust Administration | Investment Management

• The Carta Group – Premier Fee-Based Comprehensive Financial Planning

• Insurance Subsidiary• OneGroup – Personal and Commercial Lines of Insurance

12

Whole-Bank Acquisitions # of BranchesAssets

($ in millions)

June 2020 – Steuben Trust Corporation 14 (net of 11*) $608

July 2019 – Kinderhook Bank Corp 11 $643

May 2017 – Merchants Bancshares 32 $1,999

December 2015 – Oneida Financial Corp 12 $769

April 2011 – Wilber Corporation 22 $848

Branch Acquisitions # of BranchesAssets

($ in millions)

December 2013 – Bank of America 8 (net of 6*) $303

July/September 2012 – HSBC / First Niagara 19 (net of 12*) $797

STRATEGY ELEMENT #3

GROWTH MODEL: BANKING ACQUISITIONS

• Steuben Trust Corporation served Western NY for over 117 years

• Added 11 branch locations throughout Western New York

• Productive use of CBU’s strong and growing capital position

• Acquisition immediately accretive to operating EPS

In-Market Acquisition That Deepens and Extends Presence in Western NY

STEUBEN TRUST CORPORATION TRANSACTION HIGHLIGHTS – JUNE 2020

*post branch consolidations

13

STRATEGY ELEMENT #3

Employee Benefit Services Year• Fringe Benefits Design of Minnesota, Inc. 2021• HR Consultants 2018• Northeast Retirement Services / Global Trust Company 2017• EBS-RMSCO, Inc. (Actuarial Group) 2014• CAI Benefits, Inc. 2011Wealth Management Services• Steuben Trust Dept. 2020• Financial Planning Practice (Syracuse, NY) 2019• Financial Planning Practice (Liverpool/Syracuse, NY) 2019• Financial Planning Practice (Canton, NY) 2018• Financial Planning Practice (Wilkes-Barre, PA) 2017• Merchants Bank Trust Dept. 2017Insurance Services• Independent Agencies (Melbourne, FL and Boston, MA) 2021• Independent Agency (Binghamton, NY) 2018• Benefits Consulting Practice – (NYC) 2017• Independent Agencies (Hazelton, PA and Oneonta, NY) 2017• Independent Agency (Canton, NY) 2016• OneGroup – “Foundation Agency” (Syracuse, NY)(1) 2015

(1) Acquired as part of the Oneida Financial acquisition.

GROWTH MODEL: FINANCIAL SERVICES ACQUISITIONS

14

CREATING EXCESS VALUE FOR CBU’S PARTNERS AND SHAREHOLDERS

Note: Kinderhook Bank Corp (announced in January 2019) was an all-cash transaction and is excluded from the above shareholder return analysis

Source: Bloomberg, FactSet, Company filings. Market data as of July 30, 2021

Total Shareholder Return Since Announcement (including Day 1 Premium)

191% 102% 42% 20%

382%

190%

103%67%

216%

72%49%

20%0%

50%

100%

150%

200%

250%

300%

350%

400%

450%

Wilber Corporation Oneida Financial Corp Merchants Bancshares Steuben Trust Corp

CBU KBW Regional Bank Index

(October 2010) (February 2015) (October 2016) (October 2019)

Dividend Increase Since Acquisition

15

WELL DIVERSIFIED LOAN PORTFOLIO

1-4 Family Resi RE36%

1-4 Family Resi Construction

1%1-4 Family Jr Lien

1%HELOC

2%

C&I7%

PPP Loans4%

Owner Occupied

CRE9%

Non-Owner Occupied CRE13%

CRE Construction2%

Multifamily5%

Indirect Auto13%

Other Consumer4%

Agricultural1%

Other Loans2%

LOAN CUSTOMER OUTSTANDING BALANCES

June 30, 2021 call report code based customer loan data

16

• 2,571 Paycheck Protection Program (“PPP”) loans, representing $284.8 million in customer balances, were outstanding on June 30, 2021

• Loan forgiveness customer portal opened in late September 2020

• At June 30, 2021, the Company’s remaining PPP net deferred loan fees were $10.1 million

• First draw PPP net deferred loan fees were $0.9 million

• Second draw PPP net deferred loan fees were $9.2 million

PAYCHECK PROTECTION PROGRAM (PPP)

$507.2 $507.2$470.7

$410.9

$284.8

$0

$100

$200

$300

$400

$500

$600

6/30/2020 9/30/2020 12/31/2020 3/31/2021 6/30/2021

Mill

ions

PPP Loans

PPP - First Draw PPP - Second Draw

17

COVID-19 LOAN DEFERRAL UPDATE

Sector # of Loans Deferrals% of Business

Lending Deferrals

% of 6/30/21 Business Lending

Portfolio

Arts, Entertainment & Recreation1 4 $1.0 50% 0.03%

Lodging2 1 $0.5 25% 0.02%

Educational Services 1 $0.4 20% 0.01%

All Other Business Sectors 2 $0.1 5% 0.00%

Total Business Lending Deferrals 8 $2.0 100% 0.06%

Business Lending Deferral Summary by SectorJune 30, 2021 $ in Millions

(1) Arts, Entertainment & Recreation excludes Casinos(2) Lodging excludes RV Parks and Campgrounds

COVID-19 Loan Deferral Update$ in Millions

12/31/2020 3/31/2021 6/30/2021

Portfolio # of Loans Deferrals% of

12/31/20 Portfolio

# of Loans Deferrals% of

3/31/21 Portfolio

# of Loans Deferrals% of

6/30/21 Portfolio

Business Lending 63 $65.7 1.9% 42 $75.1 2.2% 8 $2.0 0.1%

Consumer Mortgage & Home Equity 9 $0.8 0.0% 5 $0.5 0.0% 4 $0.4 0.0%

Consumer Installment 2 $0.0 0.0% 0 $0.0 0.0% 0 $0.0 0.0%

Total Deferrals 74 $66.5 0.9% 47 $75.6 1.0% 12 $2.4 0.0%

18

LOW-RISK BALANCE SHEET WITH STRONG ASSET QUALITY

Source: S&P Global, Company filings.

0.34% 0.32%0.49% 0.46% 0.39% 0.34% 0.33% 0.30% 0.28% 0.25% 0.21%

0.56% 0.49%

2.19% 2.22% 2.20%

1.61%

1.25%

0.99%0.81% 0.73%

0.58% 0.52% 0.46%0.63% 0.60%

0.00%

0.50%

1.00%

1.50%

2.00%

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 YTD

CBU Peer Median

(2)

0.24% 0.21% 0.15%0.23% 0.17% 0.15% 0.15% 0.13% 0.18% 0.15% 0.12% 0.07%

(0.01%)

1.47%

1.21%

0.92%

0.61%

0.32%0.17% 0.18% 0.11% 0.13% 0.13% 0.16% 0.13% 0.10%

-0.25%

0.00%

0.25%

0.50%

0.75%

1.00%

1.25%

1.50%

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 YTDCBU Peer Median

NPAs / Assets

NCOs / Average Loans

(1) CBU as of June 30, 2021. Peer median is based on the most recent available data. Peers used throughout this presentation may be found on Appendix A

(2) During Q4 2020, the Company extended loan forbearance requests due to continued pandemic-related financial hardship and reclassified the majority of these loan relationships from accruing to nonaccrual status causing NPA levels to increase.

(1)

(1)

19

ALLOWANCE FOR CREDIT LOSSES (“ACL”) – PANDEMIC

$49.9

$55.7

$64.4 $65.0

$60.9

$55.1

$51.8

0.72%

0.81%

0.86% 0.87%

0.82%

0.75%

0.71%

0.60%

0.65%

0.70%

0.75%

0.80%

0.85%

0.90%

0.95%

1.00%

$40

$50

$60

$70

12/31/2019 3/31/2020 6/30/2020 9/30/2020 12/31/2020 3/31/2021 6/30/2021

Mill

ions

Allowance for Credit Losses (1)

Allowance for Credit Losses ACL/Loans

(1) The 12/31/2019 Allowance for Loan Losses was calculated under the Incurred Loss model while the remaining periods were calculated under the Current Expected Credit Losses (“CECL”) model.

20

CBU HAS A DIVERSIFIED, LOWER-CAPITAL INTENSITY REVENUE STREAM

CBU Peer MedianRevenue Composition (1)

Source: S&P Global, Company filings. (1) Revenue composition is based on the most recent quarter reported (Q2 2021)(2) Core ROAA shown excludes net income attributable to non controlling interest, gains on securities, non-recurring revenue/expense, amortization of intangible assets and

goodwill impairment. Adjustments were made to the 2017 peer group results for the income statement impact of the Tax Cuts and Jobs Act. (3) 2021 YTD Peer Median is based on the most recent available data. Peers used throughout presentation may be found on Appendix A.

Fee Income24%

Net Interest Income

76%

Net Interest Income

61%

0.97%1.25% 1.28%

1.19% 1.21% 1.29% 1.26% 1.25%1.39%

1.71% 1.67%

1.41% 1.47%

0.20%

0.68%

0.91% 0.96% 0.99% 1.00% 0.98% 1.00% 1.08%

1.39% 1.37%

1.03%

1.40%

0.00%

0.50%

1.00%

1.50%

2.00%

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 YTDCBU Peer Median

RESULTING IN CONSISTENT OUTPERFORMANCE

Return on Average Assets (2)

(3)

21

NET INTEREST MARGIN & RELATIVE PERFORMANCE

Net Interest Margin (FTE)

(1) The Company has maintained $1.9 billion of average cash equivalents during 2021 driving in a significant reduction in net interest margin results(2) 2021 YTD Peer Median based on most recent available data. Peers used throughout presentation may be found on Appendix A. Source: S&P Global, Company filings

3.80%

4.04% 4.07%

3.88% 3.91% 3.91%

3.73% 3.71% 3.69% 3.73% 3.76%

3.28%

2.91%

3.57%

3.84% 3.87%

3.76%

3.62%3.53%

3.43% 3.45%

3.56%3.60% 3.60%

3.29% 3.16%

2.75%

3.00%

3.25%

3.50%

3.75%

4.00%

4.25%

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021YTD

CBU Peer Median(2)

COVID Pandemic

(1)

22

CORE DEPOSIT STRENGTH AND FOCUS

30.2%

25.6%

18.6%

17.7%

7.9%

Deposit Balance Composition (1)

Demand Deposits Interest Checking Money Market Savings Time Deposits

Q2 2021 Average Cost of Deposits: 0.10%

(1) Balance composition as of 6/30/2021

23

$545$775

$988

$1,635

$2,104 $2,061

7.22%

8.38%

9.96% 10.00% 10.16%9.36%

4.74%

7.12%

8.92%

8.61%

9.92%9.02%

0%

2%

4%

6%

8%

10%

12%

14%

$0

$500

$1,000

$1,500

$2,000

2008 2011 2014 2017 2020 2Q 2021

$ in

Mill

ions

Shareholders' Equity Tier 1 Leverage Ratio Tangible Equity/Tangible Assets

STRONG CAPITAL POSITION

PCA Well-Capitalized Tier 1 Ratio

Target

(1) Tangible Equity and Tangible Assets are non-GAAP measures. Please see the Appendix for details.

(1)

24

ASSET & LIABILITY MANAGEMENT IS CONSERVATIVE

• Loan to deposit ratio of 59% as of June 30, 2021

• Investment portfolio – conservative; plain/vanilla

• 82% US Treasury Securities & Cash Equivalents at 6/30/2021

• Core deposit focused

Liquidity Sources June 30, 2021$ in Thousands

Cash and Cash Equivalents (net of float) $2,139,669

FHLB Borrowing Capacity 1,640,988

FRB Borrowing Availability 249,462

Investments1

US Gov’t & Agency 3,025,072

MBS & CMO 558,421

Municipals 406,266

Corporates 3,094

Less: Pledged Securities (1,923,120)

Net Unpledged Securities 2,069,733

Total Liquidity Sources 6,099,852

(1) Includes $31 million in unrealized losses on securities; excludes municipal qualified school construction bonds, equity securities and other investments

STRONG LIQUIDITY POSITION & SOURCES

25

HIGH-QUALITY EARNINGS AND DIVIDEND GROWTH

(1) Operating earnings excludes net of tax effect, acquisition expense, acquisition-related provision for credit losses, litigation accrual, unrealized gain on equity securities, loss on debt extinguishment, and net realized gains on securities and the $38 million positive adjustment to deferred tax expense in 2017 due to the passage of the Tax Cuts and Jobs Act. Please see Appendix for details.

(2) Per share dividend amounts equal total dividends declared in the corresponding calendar year.

(2)(1)

Source: S&P Global, Company filings

$2.19 $2.32

$3.03$3.24 $3.23

$3.08

$2.31 $2.35$2.64

$3.23 $3.29 $3.24

$1.22 $1.26 $1.32 $1.44$1.58 $1.66

$0.00

$0.50

$1.00

$1.50

$2.00

$2.50

$3.00

$3.50

$4.00

2015 2016 2017 2018 2019 2020

GAAP EPS Operating EPS Declared Dividend

2015 – 2020 GAAP EPS CAGR: 7.1%

2015 – 2020 Operating EPS CAGR: 7.0%

2015 – 2020 Dividend EPS CAGR: 6.4%Announced a $0.01 increase in quarterly

dividend from $0.42 per share to $0.43 per share on July 21, 2021

26

INVESTMENT MERITS

• Dividend Focus• 2.40% dividend yield at July 30, 2021

• Community Bank became a member of the S&P 1500 Dividend Aristocrats Index in 2012, signifying that the Company had raised its annual regular cash dividend payment for at least 20 consecutive years (now at 29 years in a row).

• Our 10-year cumulative total return to shareholders is 283% (14.4% annualized). This compares to a 10-year cumulative total return for the KBW Regional Banking Index of 192% (11.2% annualized).*

• NYSE-listed company with significant liquidity.

• Long-term growth focus. Successful and effective operating strategy. Strong fundamentals with strong asset quality. Superior return to shareholders.

*Based on 10-year historical performance through July 30, 2021, assuming dividend reinvestment.

(1) 60 trading day average as of 7/30/2021(2) S&P Global; based on the most recent available data

SHAREHOLDER PROFILE• Strong liquidity approx. 177,000 shares traded daily(1)

• Ownership(2)

• 71% Institutional‒ 39% Passive/Index ETFs‒ 29% Traditional Investment Managers ‒ 3% Government Pension Sponsors

• 29% Retail‒ 28% Public‒ 1% Insiders

27

TOTAL SHAREHOLDER RETURNS

(Through July 30, 2021 or most recent available, Including Reinvestment of Dividends)

1 Year 3 Years 5 Years 10 Years 15 Years

CBU 30.5% 6.9% 12.9% 14.4% 12.2%

S&P 600 Commercial Banks Index 59.9% 1.5% 8.9% 12.4% 3.1%

KBW Regional Bank Index 69.3% 3.0% 9.7% 11.3% 3.7%

Peer Median2 13.5% (3.8%) 6.8% 8.1% 4.0%

Prior to Financial Crisis

Source: Bloomberg

(1) Source: FactSet. Market data as of 7/30/2021 (2) Peers used throughout presentation may be found on Appendix A.

283%

118%

192%

CBU PeerMedian

KBWRegional

Bank Index

31%64% 69%

CBU PeerMedian

KBWRegional

Bank Index

1-Year10-Year 5-Year

22%

-8%

9%

CBU PeerMedian

KBWRegional

Bank Index

Total Shareholder Return1

Total Shareholder Return (annualized)1

84%39%

59%

CBU PeerMedian

KBWRegional

Bank Index

3-Year

28

0.50x1.00x1.50x2.00x2.50x3.00x3.50x4.00x

Jul 2011 Jul 2013 Jul 2015 Jul 2017 Jul 2019 Jul 2021

CBU Peer Median

WELL-DESERVED VALUATION PREMIUMPrice / Tangible Book Value

Relative Premium

Source: S&P Global. Ending share prices as of 7/30/2021

3.06x

0.00x0.20x0.40x0.60x0.80x1.00x1.20x1.40x1.60x1.80x

Jul 2011 Jul 2013 Jul 2015 Jul 2017 Jul 2019 Jul 2021

1.61x

1.45x

29

APPENDIX A

Total Assets ($000)

Market Cap of Traded

Common Equity ($M)

Peer Company Name Ticker Location MRQ 7/30/2021Webster Financial Corp. WBS Waterbury, CT 33,753,752 4,358United Bankshares Inc. UBSI Charleston, WV 27,190,926 4,463Fulton Financial Corp. FULT Lancaster, PA 26,079,774 2,497Old National Bancorp ONB Evansville, IN 23,675,666 2,667First Midwest Bancorp Inc. FMBI Chicago, IL 21,625,424 2,048Atlantic Union Bkshs Corp. AUB Richmond, VA 19,989,356 2,764Customers Bancorp Inc CUBI West Reading, PA 19,635,108 1,172WesBanco Inc. WSBC Wheeling, WV 16,966,867 2,130First Financial Bancorp. FFBC Cincinnati, OH 16,037,919 2,164First Merchants Corp. FRME Muncie, IN 14,923,097 2,198Sandy Spring Bancorp Inc. SASR Olney, MD 12,925,577 1,968Berkshire Hills Bancorp Inc. BHLB Boston, MA 12,273,325 1,364Independent Bank Corp. INDB Rockland, MA 14,194,207 2,335NBT Bancorp Inc. NBTB Norwich, NY 11,574,947 1,514First Busey Corp. BUSE Champaign, IL 12,415,449 1,329Park National Corp. PRK Newark, OH 9,947,994 1,861S&T Bancorp Inc. STBA Indiana, PA 9,495,832 1,159First Commonwealth Financial FCF Indiana, PA 9,402,402 1,267

Minimum 9,402,402 1,159Median 15,480,508 2,089

Average 17,339,312 2,181Maximum 33,753,752 4,463

Community Bank System Inc. CBU De Witt, NY 14,801,287 3,863

30

Community Bank System's management uses the term "non-GAAP" financial measures in their analysis of the company's performance and operations. Management believes that these non-GAAP financial measures helps investors and analysts measure underlying core performance and improves comparability to other organizations that have not engaged in acquisitions. These disclosures should not be viewed as a substitute for financial measures determined in accordance with GAAP, nor are they necessarily comparable to non-GAAP financial measures that may be presented by other companies. The types of non-GAAP financial measures used in this presentation include:

• Tangible equity, tangible common equity, tangible assets and tangible book value are non-GAAP financial measures which Community Bank System's management uses to assess the quality of capital and believes that investors may find useful in their analysis, although these metrics are not necessarily comparable to similar non-GAAP financial measures used by other companies. Tangible equity is calculated by excluding the balance of goodwill and other intangible assets from the calculation of total equity and adding back the amount of the deferred tax liability related to tax deductible goodwill and other intangible assets. Tangible common equity is calculated by excluding the balance of goodwill and other intangible assets from the calculation of stockholders’ equity and adding back the amount of the deferred tax liability related to tax deductible goodwill and other intangible assets. Tangible assets is calculated by excluding the balance of goodwill and other intangible assets from the calculation of total assets and adding back the amount of the deferred tax liability related to tax deductible goodwill and other intangible assets. Tangible book value per share is calculated by dividing tangible common equity by the number of shares outstanding at a point of time.

• Operating earnings is a non-GAAP financial measure which Community Bank System believes investors may find useful in their analysis. Operating earnings is calculated by excluding the one-time deferred tax expense benefits of the Tax Cuts and Jobs Act recorded in the fourth quarter of 2017, as well as acquisition-related expenses, net of tax effect, gain on sale of investments, net of tax effect, unrealized gain/loss on equity securities, net of tax effect, the gain/loss on debt extinguishment, net of tax effect, acquisition-related provision for credit losses; net of tax effect and litigation accrual, net of tax effect.

• Operating cash flow, a non-GAAP financial measure, adds back the amortization of intangibles, net of tax effect and subtracts non-impaired purchased loan accretion, net of tax effect from Operating Earnings.

• Adjusted pre-tax, pre-provision net revenues, a non-GAAP financial measure, subtracts the provision for credit losses, acquisition expenses, net gain on sale of investments, unrealized loss (gain) on equity securities, litigation accrual expenses and the gain/loss on debt extinguishment from income before tax. The Company’s management believes this information helps investors and analysts measure and compare the Company’s performance through a credit cycle by excluding the volatility in the provision for credit losses associated with the adoption of CECL and the economic uncertainty caused by the COVID-19 pandemic

RECONCILIATION OF GAAP AND NON-GAAP

31

Dollars in thousands, except per share data 2021 Years Ended Dec. 31 ($000s)

Q2 2020 2019 2018 2017 2016

Diluted Earnings per Share (GAAP) $0.88 $3.08 $3.23 $3.24 $3.03 $2.32

Operating Diluted Earnings per Share (non-GAAP) $0.88 $3.24 $3.29 $3.23 $2.64 $2.35

Net income (GAAP) $47,944 $164,676 $169,063 $168,641 $150,717 $103,812

Tax Cuts and Jobs Act deferred impact - - - - (38,010) -

Acquisition expenses, net of tax effect 3 3,942 6,952 (609) 18,309 1,146

(Gain) loss on sale of investments, net of tax effect - - (3,943) - (1) -

Unrealized (gain) loss on equity securities, net of tax effect - 5 (15) (520) - -

(Gain) loss on debt extinguishment, net of tax effect - (336) - 252 - -

Acquisition-related provision for credit losses; net of tax effect - 2,446 - - - -

Litigation accrual, net of tax effect - 2,357 - - - -

Operating Net Income (non-GAAP) 47,947 173,090 172,057 167,764 131,015 104,958

Amortization of intangibles, net of tax effect 2,496 11,425 12,886 14,375 11,936 3,679

Subtotal (non-GAAP) 50,443 184,515 184,943 182,139 142,951 108,637

Acquired non-impaired loan accretion, net of tax effect (899) (4,388) (4,981) (6,272) (4,149) (1,926)

Adjusted Net Income (non-GAAP) 49,544 180,127 179,962 175,867 138,802 106,711

Cash Dividends Paid 22,609 87,131 80,241 71,495 62,305 55,048

Cash Dividend % of Adjusted Net Income 46% 48% 45% 41% 45% 52%

CBU FREE CASH FLOW

32

Dollars in thousands, except per share data Q2 2021 2020 2017 2014 2011 2008

Total assets

Total assets (GAAP) $14,801,287 $13,931,094 $10,746,198 $7,489,440 $6,488,275 $5,174,552

Intangible assets (842,672) (846,648) (825,088) (386,973) (360,564) (328,624)

Deferred taxes on intangible assets 44,072 44,370 48,419 35,842 24,308 14,216

Total tangible assets (non-GAAP) 14,002,687 13,128,816 9,969,529 7,138,309 6,152,019 4,860,144

Total common equity

Shareholders' Equity (GAAP) 2,061,100 2,104,107 1,635,315 987,904 774,583 544,651

Intangible assets (842,672) (846,648) (825,088) (386,973) (360,564) (328,624)

Deferred taxes on intangible assets 44,072 44,370 48,419 35,842 24,308 14,216

Total tangible common equity (non-GAAP) 1,262,500 1,301,829 858,646 636,773 438,327 230,243

Net tangible equity-to-assets ratio at quarter end

Total tangible common equity (non-GAAP) - numerator $1,262,500 $1,301,829 $858,646 $636,773 $438,327 $230,243

Total tangible assets (non-GAAP) - denominator 14,002,687 13,128,816 9,969,529 7,138,309 6,152,019 4,860,144

Net tangible equity-to-assets ratio at period end (non-GAAP) 9.02% 9.92% 8.61% 8.92% 7.12% 4.74%

TANGIBLE EQUITY COMPONENTS

33

Dollars and shares in thousands, except per share data YTD 2021 YTD 2020 Q2 2021 Q1 2021 Q4 2020 Q3 2020 Q2 2020

Pre-tax, pre-provision net revenue

Net income (GAAP) $100,794 $75,382 $47,944 $52,850 $46,485 $42,809 $35,248

Income taxes 26,524 18,249 14,416 12,108 12,247 10,904 8,964

Income before income taxes 127,318 93,631 62,360 64,958 58,732 53,713 44,212

Provision for credit losses (10,057) 15,368 (4,338) (5,719) (3,101) 1,945 9,774

Pre-tax, pre-provision net revenue (non-GAAP) 117,261 108,999 58,022 59,239 55,631 55,658 53,986

Acquisition expenses 31 3,741 4 27 396 796 3,372

Gain on sale of investments, net 0 0 0 0 0 0 0

Unrealized loss (gain) on equity securities (24) 18 0 (24) (24) 12 (12)

Litigation accrual 0 0 0 0 0 2,950 0

Gain on debt extinguishment 0 0 0 0 (421) 0 0

Adjusted pre-tax, pre-provision net revenue (non-GAAP) $117,268 $112,758 $58,026 $59,242 $55,582 $59,416 $57,346

Pre-tax, pre-provision net revenue per share

Diluted earnings per share (GAAP) $1.85 $1.43 $0.88 $0.97 $0.86 $0.79 $0.66

Income taxes 0.49 0.34 0.26 0.22 0.22 0.20 0.17

Income before income taxes 2.34 1.77 1.14 1.19 1.08 0.99 0.83

Provision for credit losses (0.19) 0.29 (0.08) (0.10) (0.04) 0.04 0.19

Pre-tax, pre-provision net revenue per share (non-GAAP) 2.15 2.06 1.06 1.09 1.04 1.03 1.02

Acquisition expenses 0.00 0.07 0.00 0.00 0.00 0.02 0.06

Gain on sale of investments 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Unrealized (gain) loss on equity securities 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Litigation accrual 0.00 0.00 0.00 0.00 0.00 0.05 0.00

Gain on debt extinguishment 0.00 0.00 0.00 0.00 (0.01) 0.00 0.00

Adjusted pre-tax, pre-provision net revenue per share (non-GAAP) $2.15 $2.13 $1.06 $1.09 $1.03 $1.10 $1.08

PRE-TAX, PRE-PROVISION COMPONENTS

Investor Relations ContactMr. Joseph E. SutarisEVP & Chief Financial OfficerJoseph.Sutaris@cbna.com(315) 445 - 7396