Company: OSBC
Filing Date: 2025-05-06
Form Type: S-4/A
Source: 0001104659-25-045103
Chunk: 435

Company: OLD SECOND BANCORP INC
Filing Date: 2025-05-06
Form: S-4/A
Chunk 435
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| ​ |     5.1 | ​ | ​ | Opinion of Nelson Mullins Riley and Scarborough LLP regarding the legality of the securities being registered.*                                                                                                                                                                                          | ​ |
| ​ |     8.1 | ​ | ​ | Opinion of Nelson Mullins Riley and Scarborough LLP regarding certain U.S. federal income tax aspects of the merger.**                                                                                                                                                                                   | ​ |
| ​ |     8.2 | ​ | ​ | Opinion of Vedder Price P.C. regarding certain U.S. federal income tax aspects of the merger.**                                                                                                                                                                                                          | ​ |
| ​ |    23.1 | ​ | ​ | Consent of Plante & Moran PLLC, independent registered public accounting firm of Old Second Bancorp, Inc.**                                                                                                                                                                                              | ​ |
| ​ |    23.2 | ​ | ​ | Consent of RSM US LLP, independent auditor of Bancorp Financial, Inc.**                                                                                                                                                                                                                                  | ​ |
| ​ |    23.3 | ​ | ​ | Consent of Nelson Mullins Riley and Scarborough LLP (included in Exhibits 5.1* and 8.1** hereto).                                                                                                                                                                                                        | ​ |
| ​ |    23.4 | ​ | ​ | Consent of Vedder Price P.C. (included in Exhibit 8.2 hereto).**                                                                                                                                                                                                                                         | ​ |
| ​ |      24 | ​ | ​ | Power of Attorney (included on signature page).*                                                                                                                                                                                                                                                         | ​ |
| ​ |    99.1 | ​ | ​ | Consent of Keefe, Bruyette & Woods, Inc.*                                                                                                                                                                                                                                                                | ​ |
| ​ |    99.2 | ​ | ​ | Consent of Darin Campbell to be named as director.*                                                                                                                                                                                                                                                      | ​ |
| ​ |    99.3 | ​ | ​ | Form of Proxy Card to be used by Bancorp Financial.**                                                                                                                                                                                                                                                    | ​ |
| ​ |     107 | ​ | ​ | Filing Fee Table.*                                                                                                                                                                                                                                                                                       | ​ |

* Previously filed ** Filed herewith.

II-2

TABLE OF CONTENTS

†

Pursuant to Item 601(b)(2) of Regulation S-K, Old Second agrees to furnish supplementally a copy of any omitted schedule or exhibit to the Agreement and Plan of Merger to the SEC on a confidential basis upon request.

## ITEM 22.   UNDERTAKINGS.
The undersigned registrant hereby undertakes:

(