X0609 4 2021-05-11 0000357173 OLD SECOND BANCORP INC OSBC 0001244438 YORK JILL E false 37 S. RIVER ST. AURORA IL 60506 true false false false 0 Old Second Bancorp, Inc. Common Stock 2021-05-11 4 L 0 14.2083 14.08 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2021-08-11 4 L 0 17.5446 11.44 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2021-11-09 4 L 0 14.5974 13.81 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2022-02-08 4 L 0 14.0252 14.43 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2022-05-10 4 L 0 14.3579 14.14 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2022-08-09 4 L 0 14.5777 13.98 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2022-11-08 4 L 0 12.0515 16.97 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2023-02-07 4 L 0 11.9166 17.21 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2023-05-09 4 L 0 18.4285 11.16 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2023-08-08 4 L 0 12.9172 15.99 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2023-11-07 4 L 0 14.5225 14.27 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2024-02-06 4 L 0 15.4522 13.46 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2024-05-06 4 L 0 14.46 14.43 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2024-08-05 4 L 0 14.0955 14.86 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2024-11-04 4 L 0 15.6156 16.15 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2025-02-10 4 L 0 13.3087 19.02 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2025-05-05 4 L 0 15.5779 16.30 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2025-08-04 4 L 0 15.3405 16.61 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2025-11-10 4 L 0 16.2619 18.35 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2026-02-09 4 L 0 14.1217 21.21 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2026-05-11 4 L 0 14.3767 20.90 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 2026-08-10 4 L 0 11.8801 25.38 A 4319.6382 D Old Second Bancorp, Inc. Common Stock 15430 I Living Trust Restricted Stock Units 10595 D Represents shares acquired through the automatic reinvestment of cash dividends paid on shares of the Issuer's common stock held in the Reporting Person's individual retirement account, under a dividend reinvestment feature offered by the account custodian. The custodian's reinvestment feature is not a plan sponsored by the Issuer. These acquisitions were not previously reported because of an administrative oversight, and are reported herein to correct the omission. The amount of securities beneficially owned represents the Reporting Person's holdings in her individual retirement account as of the date hereof, after giving effect to all dividend reinvestment transactions reported herein. The transactions reported herein were not previously reported. The Reporting Person additionally beneficially owns 15,430 shares through her living trust as of October 15, 2026. This amount reflects her current trust holdings and supersedes the trust balance previously reported. /s/ Shirley Cantrell, Attorney-in-Fact 2026-10-21