GARY S. COLLINS - 17 Feb 2026 Form 4 Insider Report for OLD SECOND BANCORP INC (OSBC)

Role: VICE CHAIRMAN, Director
Signature: /s/ Shirley Cantrell, Attorney-in-Fact
Issuer symbol: OSBC
Transactions as of: 17 Feb 2026
Net transactions value: -$57,267
Form type: 4
Filing time: 24 Feb 2026, 18:59:22 UTC
Previous filing: 05 Jan 2026
Next filing: 04 Mar 2026
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
COLLINS GARY S	VICE CHAIRMAN, Director	37 S. RIVER ST., AURORA	/s/ Shirley Cantrell, Attorney-in-Fact	24 Feb 2026	0001184766

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	OSBC	Restricted Stock Units	Award	$0	+8,858	+20%	$0.000000	53,804	17 Feb 2026	Direct	F1
transaction	OSBC	Restricted Stock Units	Tax liability	$57,267	-2,784	-5.8%	$20.57	45,558	21 Feb 2026	Direct	F2
holding	OSBC	Old Second Bancorp, Inc. Common Stock						5,462	17 Feb 2026	Direct	F3
holding	OSBC	Old Second Bancorp, Inc. Common Stock						46,624	17 Feb 2026	Direct	F4
holding	OSBC	Old Second Bancorp, Inc. Common Stock						78,256	17 Feb 2026	IRA	F5
holding	OSBC	Old Second Bancorp, Inc. Common Stock						6,805	17 Feb 2026	By 401-K

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Each restricted stock unit represents a contingent right to receive one share of common stock. The reporting person was granted 8,858 restricted stock units on the date of the grant, 4,429 of which are time-based restricted stock units that vest on the third anniversary of the grant date, and 4,429 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 8,246 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. Collin's name outright.
F4	These shares are held in Mr. Collin's name in a brokerage account.
F5	Included in this total are 41,000 shares in a ROTH IRA and 37,256.085 in a traditional IRA.