NorthWestern Energy Group, Inc.

(a) Exhibits

Exhibit 2.1 — Agreement and Plan of Merger, dated as of August 18, 2025, by and among Black Hills Corporation, NorthWestern Energy Group, Inc., and River Merger Sub Inc.(incorporated by reference to Exhibit 2.1 of NorthWestern Energy Group's Current Report on Form 8-K, dated August 18, 2025, Commission File No. 000-56598).*

Exhibit 3.1— Second Amended and Restated Bylaws of NorthWestern Energy Group, Inc., dated August 18, 2025 (incorporated by reference to Exhibit 10.1 of NorthWestern Energy Group's Current Report on Form 8-K, dated August 18, 2025, Commission File No. 000-56598).

Exhibit 10.1 — Chief Executive Officer Agreement, dated August 18, 2025, between Black Hills Corporation and Brian B. Bird dated August 18, 2025 (incorporated by reference to Exhibit 10.1 of NorthWestern Energy Group's Current Report on Form 8-K, dated August 18, 2025, Commission File No. 000-56598).

Exhibit 10.2 —Amendment No. 3 to Term Loan Credit Agreement and Lender Joinder Agreement. (incorporated by reference to Exhibit 10.1 of NorthWestern Energy Group's Current Report on Form 8-K, dated October 3, 2025, Commission File No. 000-56598).

Exhibit 31.1 — Certification of chief executive officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 - NorthWestern Energy Group, Inc.

Exhibit 31.2 — Certification of chief financial officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 - NorthWestern Energy Group, Inc.

Exhibit 32.1 — Certification of chief executive officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 - NorthWestern Energy Group, Inc.

Exhibit 32.2 — Certification of chief financial officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 - NorthWestern Energy Group, Inc.

Exhibit 101.INS—Inline XBRL Instance Document - the instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the Inline XBRL document.

Exhibit 101.SCH—Inline XBRL Taxonomy Extension Schema Document

Exhibit 101.CAL—Inline XBRL Taxonomy Extension Calculation Linkbase Document

Exhibit 101.DEF—Inline XBRL Taxonomy Extension Definition Linkbase Document

Exhibit 101.LAB—Inline XBRL Taxonomy Label Linkbase Document

Exhibit 101.PRE—Inline XBRL Taxonomy Extension Presentation Linkbase Document

Exhibit 104 Cover Page Interactive Data File (formatted as Inline XBRL and contained in Exhibit 101)

*Schedules and Exhibits have been omitted pursuant to Item 601(b)(2) of Regulation S-K. The registrant hereby agrees to supplementally furnish to the SEC upon request any omitted schedule or exhibit to the Agreement and Plan of Merger.

**Certain personal information in this exhibit has been omitted in accordance with Regulation S-K Item 601(a)(6).