OLD SECOND BANCORP INC — Director's Dealing 2026

Feb 24, 2026

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: OLD SECOND BANCORP INC (OSBC)
CIK: 0000357173
Period of Report: 2026-02-17

Reporting Person: Pilmer Donald (N/A)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2026-02-17	Restricted Stock Units	A	11292	—	Acquired	50010	Direct
2026-02-21	Restricted Stock Units	F	1818	$20.57	Disposed	44754	Direct

Holdings (Non-Derivative)

Security	Shares	Ownership
Old Second Bancorp, Inc. Common Stock	3438	Direct
Old Second Bancorp, Inc. Common Stock	63135	Direct
Old Second Bancorp, Inc. Common Stock	4010	Indirect
Old Second Bancorp, Inc. Common Stock	182	Indirect
Old Second Bancorp, Inc. Common Stock	1450	Indirect

Footnotes

F1: Each restricted stock unit represents a contingent right to receive one share of common stock. The reporting person was granted 11,292 restricted stock units on the date of the grant, 5,646 of which are time-based restricted stock units that vest on the third anniversary of the grant date, and 5,646 of which are performance-based restricted stock units that may vest and convert to shares within a range from 0% to 175% of the underlying performance-based restricted stock units originally awarded, depending on our compensation committee approved performance metrics. Vested shares, if any, will be delivered to the reporting person in 3 to 5 business days from the date of vesting.

F2: Represents shares withheld by the issuer to satisfy applicable tax withholding obligations in connection with the vesting of 5,256 previously reported time-based restricted stock units, the remaining shares of which were issued and added to the reporting person's common stock holdings.

F3: These shares are held in Mr. Pilmer's name outright.

F4: These shares are held in spouse's IRA for which Mr. Pilmer is listed as a beneficiary.