Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION FORM 10-K Washington, D.C. 20549 (Mark One) 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 0-6233 (Exact name of registrant as specified in its charter) 1st Source Corporation 35-1068133 (I.R.S. Employer Identification No.) Indiana (State or other jurisdiction of incorporation or organization) 100 North Michigan Street South Bend, IN (Address of principal executive offices) 46601 (Zip Code) Registrant’s telephone number, including area code:  (574) 235-2000 Securities registered pursuant to Section 12(b) of the Act: Title of each class Common Stock — without par value Trading Symbol(s) SRCE Name of each exchange on which registered The NASDAQ Stock Market LLC Securities registered pursuant to Section 12(g) of the Act:  None Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes o No x 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 o No x 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 x No o 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 x No o 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. Large accelerated filer x Non-accelerated filer ☐ 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. o 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 x Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes ☐ No x The aggregate market value of the voting common stock held by non-affiliates of the registrant as of June 30, 2020 was $695,302,047 The number of shares outstanding of each of the registrant’s classes of stock as of February 12, 2021: Common Stock, without par value — 25,301,678 shares Portions of the 2021 Proxy Statement for the 2021 annual meeting of shareholders to be held April 22, 2021, are incorporated by reference into Part III. DOCUMENTS INCORPORATED BY REFERENCE