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Table of Contents 0 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 Delaware ( State of Incorporation ) Commission file number 0-10537 Old Second Bancorp , Inc. Large accelerated filer Non - accelerated filer 37 South River Street , Aurora , Illinois 60507 ( Address of principal executive offices , including zip code ) Title of Class Common Stock , $ 1.00 par value 36-3143493 ( IRS Employer Identification Number ) ( 630 ) 892-0202 ( Registrant's telephone number , including Area Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) OSBC Securities registered pursuant to Section 12 ( g ) of the Act : None ( Title of Class ) Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Name of each exchange on which registered The Nasdaq Stock Market Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange 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 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 Accelerated filer Smaller reporting company Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , 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 . 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 . Indicate by check mark whether the registrant is a shell company ( as defined in Exchange Act Rule 12b - 2 ) . Yes No ™ The aggregate market value of the voting and non - voting common equity held by non - affiliates of the registrant , on June 30 , 2020 , the last business day of the registrant's most recently completed second fiscal quarter , was approximately $ 224.8 million . The number of shares outstanding of the registrant's common stock , par value $ 1.00 per share , was 29,125,741 at March 4 , 2021 . DOCUMENTS INCORPORATED BY REFERENCE : Certain information required by Part III of this Annual Report on Form 10 - K is incorporated by reference from the registrant's definitive proxy statement relating to the 2020 Annual Meeting of Stockholders , which will be filed with the Securities and Exchange Commission within 120 days after the end of the fiscal year to which this Annual Report on Form 10 - K relates .