Company: OSBC
Filing Date: 2025-05-08
Form Type: 424B3
Source: 0001104659-25-046065
Chunk: 7

Company: OLD SECOND BANCORP INC
Filing Date: 2025-05-08
Form: 424B3
Chunk 7
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 par value $1.00 per share, and all references in this proxy statement/prospectus to “Bancorp Financial common stock” refer to the common stock of Bancorp Financial, par value $1.00 per share.

Any reference to “Old Second stockholders” or to the stockholders of Old Second refer to the stockholders of Old Second.

All references in this proxy statement/prospectus to the “merger agreement” refer to the Agreement and Plan of Merger dated February 24, 2025, by and between Old Second and Bancorp Financial, as it may be amended from time to time. All references in this proxy statement/prospectus to “we,” “our” and “us” refer to Old Second and Bancorp Financial collectively, unless otherwise indicated or as the context requires.

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TABLE OF CONTENTS

TABLE OF CONTENTS

| ​                                                                                       | ​ | ​ | Page |   |    |   | ​ |
| WHERE YOU CAN FIND MORE INFORMATION                                                     | ​ | ​ | ​    | ​ |  i | ​ | ​ |
| ABOUT THIS PROXY STATEMENT/PROSPECTUS                                                   | ​ | ​ | ​    | ​ | ii | ​ | ​ |
| QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETING                          | ​ | ​ | ​    | ​ |  1 | ​ | ​ |
| SUMMARY                                                                                 | ​ | ​ | ​    | ​ |  8 | ​ | ​ |
| CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS                               | ​ | ​ | ​    | ​ | 16 | ​ | ​ |
| RISK FACTORS                                                                            | ​ | ​ | ​    | ​ | 19 | ​ | ​ |
| BANCORP FINANCIAL SPECIAL MEETING OF STOCKHOLDERS                                       | ​ | ​ | ​    | ​ | 27 | ​ | ​ |
| Date, Time and Place of the Bancorp Financial Special Meeting                           | ​ | ​ | ​    | ​ | 27 | ​ | ​ |
| Purpose of Bancorp Financial Special Meeting                                            | ​ | ​ | ​    | ​ | 27 | ​ | ​ |
| Recommendation of the Bancorp Financial Board of Directors                              | ​ | ​ | ​    | ​ | 27 | ​ | ​ |
| Bancorp Financial Record Date; Stockholders Entitled to Vote                            | ​ | ​ | ​    | ​ |