X0609 4 2026-09-30 0000357173 OLD SECOND BANCORP INC OSBC 0001184766 COLLINS GARY S false 37 S. RIVER ST. AURORA IL 60302 true true false false VICE CHAIRMAN 0 Old Second Bancorp, Inc. Common Stock 2026-09-30 4 J 0 30 0 A 7125 I By 401-K Old Second Bancorp, Inc. Common Stock 14136 D Old Second Bancorp, Inc. Common Stock 53136.0850 I IRA Restricted Stock Units 37312 D These shares were allocated during the third quarter pursuant to the Old Second Bancorp, Inc. Employee Savings Plan & Trust. Information herein was provided by the Plan Trustee as of 9-30-26. Included in this total are 30,880 shares in a ROTH IRA and 22,256.085 in a traditional IRA. /s/ Shirley Cantrell, Attorney-in-Fact 2026-10-01