Company: FRME
Filing Date: 2025-09-25
Form Type: 425
Source: 0001193125-25-216443
Chunk: 0

Company: FIRST MERCHANTS CORP
Filing Date: 2025-09-25
Form: 425
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, DC 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 DATE OF REPORT (Date of earliest event reported): September 24, 2025 Commission File Number 0-17071 FIRST MERCHANTS CORPORATION (Exact name of registrant as specified in its charter)

| INDIANA                      |     | 35-1544218         |
| (State or other jurisdiction 
 of incorporation)            |     | -IRS Employer      
 Identification No. |

200 East Jackson Street P.O. Box 792 Muncie, IN 47305-2814 (Address of principal executive offices, including zip code) (765) 747-1500 (Registrant’s telephone number, including area code) Not Applicable (Former name or former address, if changed since last report)

| Title of Each Class                         |     | Trading   
 Symbol(s) |     | Name of each exchange       
 on which registered         |
| Common Stock, $0.125 stated value per share |     | FRME      |     | Nasdaq Global Select Market |

Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ☒ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |

| ☐ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 
 CFR 240.14a-12)                                                        |

| ☐ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |

| ☐ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2of the Securities Exchange Act of 1934 (§240.12b-2of this chapter). 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