Old Second Bancorp Inc 2025年度报告

SECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 Form 11-K ANNUAL REPORT Pursuant to Section 15 (d) of the Securities Exchange Act of 1934 ANNUAL REPORT PURSUANT TO SECTION 15(d) OFTHE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December31,2025 OR TRANSITION REPORT PURSUANT TO SECTION 15(d) OFTHE SECURITIES EXCHANGE ACT OF 1934 For the transition period fromto ____________ Commission file number0-10537 A. Full title of the plan and the address of the plan if different from that of the issuer named below: Old Second Bancorp, Inc. Employees’ 401(k) Savings Plan and Trust B. Name of the issuer of the securities held pursuant to the plan and the address of its principalexecutive office: 37 South River Street, Aurora, Illinois 60507(Address of principal executive offices, including zip) (630) 892-0202(Registrant’s telephone number, including Area Code) Financial Statements and Supplemental Schedule Old Second Bancorp, Inc. Employees’401(k) Savings Plan and Trust As of December31,2025 and 2024, and the year ended December31,2025 withReport of Independent Registered Public Accounting Firm Employer Identification #36-3143493Plan #003 Old Second Bancorp, Inc. Employees’401(k) Savings Plan and Trust Financial Statements and Supplemental Schedule As of December31,2025 and 2024, and the year ended December31,2025 Contents Report of Independent Registered Public Accounting Firm4 Financial StatementsStatements of Net Assets Available for Benefits5Statement of Changes in Net Assets Available for Benefits6Notes to Financial Statements7-11 Supplemental ScheduleSchedule H, Line 4i – Schedule of Assets (Held at End of Year)13 Consent of Independent Registered Public Accounting Firm14 Report of Independent Registered Public Accounting Firm To the Plan Administrator and Plan ParticipantsOld Second Bancorp, Inc. Employees’401(k) Savings Plan and Trust Opinion on the Financial Statements We have audited the accompanying statements of net assets available for benefits of Old Second Bancorp,Inc. Employees’ 401(k) Savings Plan and Trust (the “Plan”) as of December31,2025 and 2024; the relatedstatement of changes in net assets available for benefits for the year ended December31,2025; and therelated notes (collectively referred to as the “financial statements”). In our opinion, the financial statementspresent fairly, in all material respects, the net assets of the Plan as of December31,2025 and 2024 and thechanges in its net assets for the year ended December31,2025 in conformity with accounting principlesgenerally accepted in the United States of America. Basis of Opinion The Plan’s management is responsible for these financial statements. Our responsibility is to express anopinion on the Plan’s financial statements based on our audits. We are a public accounting firm registeredwith the Public Company Accounting Oversight Board (United States) (the “PCAOB”) and are required to beindependent with respect to the Plan in accordance with U.S. federal securities laws and the applicable rulesand regulations of the Securities and Exchange Commission and the PCAOB. We conducted our audits in accordance with the standards of the PCAOB. Those standards require that weplan and perform the audits to obtain reasonable assurance about whether the financial statements are free ofmaterial misstatement, whether due to error or fraud. The Plan is not required to have, nor were we engagedto perform, an audit of its internal control over financial reporting. As part of our audits, we are required toobtain an understanding of internal control over financial reporting but not for the purpose of expressing anopinion on the effectiveness of the Plan’s internal control over financial reporting. Accordingly, we expressno such opinion. Our audits included performing procedures to assess the risks of material misstatement of the financialstatements, whether due to error or fraud, and performing procedures that respond to those risks. Suchprocedures included examining, on a test basis, evidence regarding the amounts and disclosures in thefinancial statements. Our audits also included evaluating the accounting principles used and significantestimates made by management, as well as evaluating the overall presentation of the financial statements. Webelieve that our audits provide a reasonable basis for our opinion. Supplemental Information Thesupplemental information in the accompanying schedule of assets(held at end of year)as ofDecember31,2025 has been subjected to audit procedures performed in conjunction with the audit of thePlan’s financial statements. The supplemental information is the responsibility of the Plan’s management.Our audit procedures included determining whether the supplemental information reconciles to the financialstatements or the underlying accounting and other records, as applicable, and performing procedures to testthe completeness and accuracy of the information presented in the