Company: OSBC
Filing Date: 2025-05-08
Form Type: 424B3
Source: 0001104659-25-046065
Chunk: 8

Company: OLD SECOND BANCORP INC
Filing Date: 2025-05-08
Form: 424B3
Chunk 8
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 because the information in this section may not provide all the information that might be important to you in determining how to vote. Additional important information is also contained in the annexes to, and the documents incorporated by reference in, this proxy statement/prospectus.

#### Q:   What is the merger?
A:

Old Second and Bancorp Financial have entered into an Agreement and Plan of Merger, dated as of February 24, 2025. Under the merger agreement, Bancorp Financial will merge with and into Old Second, with Old Second continuing as the surviving entity, in a transaction we refer to as the “merger.” Immediately following the merger, Evergreen Bank Group, Bancorp Financial’s wholly owned bank subsidiary, will merge with and into Old Second National Bank, Old Second’s wholly owned bank subsidiary, with Old Second National Bank as the surviving bank, in a transaction we refer to as the “bank merger.”

Bancorp Financial will hold a special meeting of its stockholders, which we refer to as the “Bancorp Financial special meeting,” to obtain the required stockholder approval, and you are being provided with this proxy statement/prospectus in connection with that meeting.

A copy of the merger agreement is attached to this proxy statement/prospectus as Annex A. We urge you to carefully read this proxy statement/prospectus, the annexes to, and the documents incorporated by reference in, this proxy statement/prospectus.

#### Q:   Why am I receiving this document?
A:

In order to complete the merger, Bancorp Financial stockholders must approve the merger proposal and terminate the Stockholders Agreement, which will be effected by approving the stockholders agreement amendment proposal, as further described below.

**Old Second and Bancorp Financial are sending this proxy statement/prospectus to Bancorp Financial’s stockholders to help them decide how to vote their shares of common stock with respect to the merger proposal and the stockholders agreement amendment proposal.

Information about the Bancorp Financial special meeting, the merger and the other business to be considered at such special meeting is contained in this proxy statement/prospectus and you should read it carefully.

This document constitutes both a proxy statement of Bancorp Financial and a prospectus of Old Second. It is a proxy statement because the board of directors of Bancorp Financial is soliciting proxies from its stockholders using this document. It is a prospectus because Old Second, in connection with the merger, will issue shares of Old Second common stock to Bancorp Financial stockholders, and this proxy statement