Sec Form 4 Filing - COLLINS GARY S @ OLD SECOND BANCORP INC - 2024-03-13

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person COLLINS GARY S 2. Issuer Name and Ticker or Trading Symbol OLD SECOND BANCORP INC [ OSBC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) VICE CHAIRMAN (Last) (First) (Middle) 37 S. RIVER ST. 3. Date of Earliest Transaction (MM/DD/YY) 03/13/2024 (Street) AURORA, IL60302 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Old Second Bancorp, Inc. Common Stock 03/13/2024 A 15,924 ( 1 ) A $ 0 15,924 D Old Second Bancorp, Inc. Common Stock 03/13/2024 F 4,665 ( 2 ) D $ 13.36 6,594 D Old Second Bancorp, Inc. Common Stock 11,259 D Restricted Stock Units 33,838 ( 3 ) D Old Second Bancorp, Inc. Common Stock 92,893.306 ( 4 ) D Old Second Bancorp, Inc. Common Stock 76,768.085 ( 5 ) I IRA Old Second Bancorp, Inc. Common Stock 5,894 I By 401-K

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other COLLINS GARY S 37 S. RIVER ST. AURORA, IL60302 X VICE CHAIRMAN Signatures /s/ Shirley Cantrell, Attorney-in-Fact 03/15/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Shares delivered to the reporting person pursuant to vesting of performance-based restricted stock units granted under the Old Second Bancorp, Inc. 2019 Equity Incentive Plan, as Amended and Restated and vested upon achievement of performance goals for the applicable performance period. At the time of grant, the reporting person reported an acquisition of 10,616 of these shares, which represented the number of shares that would be delivered if target performance was achieved during the performance period. Actual performance exceeded the target performance for the performance period. ( 2 )Shares withheld for taxes upon settlement in shares of the performance-based restricted stock units previously granted to the reporting person. ( 3 )Included in this total are 16,919 shares of time-based unvested restricted stock units and 16,919 shares of performance-based restricted stock units (representing the number of unvested performance-based restricted stock units that will vest if target performance is achieved). ( 4 )Included in this total are 41,762 shares held jointly with child and 51,131.306 shares held jointly with a child at a broker. ( 5 )Included in this total are 41,000 shares in a ROTH IRA and 35,768.085 in a traditional IRA.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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