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Table of Contents ( Mark One ) UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 Form 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR □ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 000-26481 FINANCIAL INSTITUTIONS , INC . ( Exact name of registrant as specified in its charter ) NEW YORK ( State or other jurisdiction of incorporation or organization ) 220 LIBERTY STREET , WARSAW , NEW YORK ( Address of principal executive offices ) Registrant's telephone number , including area code : Securities registered under Section 12 ( b ) of the Exchange Act : Title of each class Common stock , par value $ 0.01 per share Large accelerated filer Non - accelerated filer Trading Symbol ( s ) FISI 16-0816610 ( I.R.S. Employer Identification No. ) ( 585 ) 786-1100 14569 ( ZIP Code ) Name of exchange on which registered Nasdaq Global Select Market NONE Yes No Securities registered under Section 12 ( g ) of the Exchange Act : Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes No Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company ” and “ emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company ✓ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Yes No Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . The aggregate market value of the registrant's common stock , par value $ 0.01 per share , held by non - affiliates of the registrant , as computed by reference to the June 30 , 2020 closing price reported by Nasdaq , was approximately $ 292,245,000 . As of February 28 , 2021 , there were outstanding , exclusive of treasury shares , 15,816,318 shares of the registrant's common stock . DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's proxy statement for the 2021 Annual Meeting of Shareholders are incorporated by reference in Part III of this Annual Report on Form 10 - K .