Company: OSBC
Filing Date: 2025-06-02
Form Type: S-8
Source: 0000357173-25-000052
Chunk: 0

Company: OLD SECOND BANCORP INC
Filing Date: 2025-06-02
Form: S-8
Chunk 0
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As filed with the Securities and Exchange Commission on June 2, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 OLD SECOND BANCORP, INC. (Exact name of registrant as specified in its charter)

| ​                               | ​​ | ​​                                  |
| Delaware                        |    | 36-3143493                          |
| (State or other jurisdiction of 
 incorporation or organization)  |    | -I.R.S. Employer Identification No. |

37 South River Street Aurora, Illinois 60507(Address of principal executive offices) (Zip Code) Old Second Bancorp, Inc. 2019 Equity Incentive Plan, as Amended and Restated (Full title of the Plan) James L. Eccher Chairman, President and Chief Executive Officer Old Second Bancorp, Inc. 37 South River Street Aurora, Illinois 60507 (Name and address of agent for service) (630) 892-0202 (Telephone number, including area code, of agent for service) Copies to: J. Brennan Ryan Brittany M. McIntosh Nelson Mullins Riley & Scarborough, LLP 201 17th Street NW, Suite 1700 Atlanta, Georgia 30363 Telephone: (404) 322-6000 Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

| ​                       | ​ | ​                         | ​ |
| Large accelerated filer | ◻ | Accelerated filer         | ⌧ |
| Non-accelerated filer   | ◻ | Smaller reporting company | ◻ |
| ​                       | ​ | Emerging growth company   | ◻ |

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ◻

EXPLANATORY NOTE Old Second Bancorp, Inc. (“we,” “our,” “us,” “Registrant” or the