Nineteenth Supplemental Indenture, dated as of June 1, 2023, between the Company and The Bank of New York Mellon, as trustee

THIS NINETEENTH SUPPLEMENTAL INDENTURE, dated as of June 1, 2023 (the “Supplemental Indenture”), is made by and between NORTHWESTERN CORPORATION (formerly known as NorthWestern Public Service Company), a corporation organized and existing under the laws of the State of Delaware (the “Company”), the post office address of which is 3010 West 69th Street, Sioux Falls, South Dakota 57108, and THE BANK OF NEW YORK MELLON (formerly known as The Bank of New York (successor to JPMorgan Chase Bank, N.A. (successor by merger to The Chase Manhattan Bank (National Association)))) (the “Trustee”), as Trustee under the General Mortgage Indenture and Deed of Trust dated as of August 1, 1993, hereinafter mentioned, the post office address of which is 240 Greenwich Street, 7E, New York, New York 10286;

WHEREAS, the Company has heretofore executed and delivered its General Mortgage Indenture and Deed of Trust dated as of August 1, 1993 (the “Original Indenture”), to the Trustee, for the security of the Bonds of the Company issued and to be issued thereunder (the “Bonds”); and

WHEREAS, the Company has heretofore executed and delivered to the Trustee eighteen indentures supplemental to the Original Indenture, the first dated as of August 15, 1993, the second dated as of August 1, 1995, each of the third, fourth and fifth dated as of September 1, 1995, the sixth dated as of February 1, 2003, the seventh dated as of November 1, 2004, the eighth dated as of May 1, 2008, the ninth dated as of May 1, 2010, the tenth dated as of August 1, 2012, the eleventh dated as of December 1, 2013, the twelfth dated as of December 1, 2014, the thirteenth dated as of September 1, 2015, the fourteenth dated as of June 1, 2016, the fifteenth dated as of September 1, 2016, the sixteenth dated as of April 1, 2020, the seventeenth dated as of March 1, 2023, and the eighteenth dated as of May 1, 2023 (the Original Indenture, as supplemented and amended by the aforementioned seventeen supplemental indentures and by this Supplemental Indenture, being hereinafter referred to as the “Indenture”); and

WHEREAS, pursuant to and in accordance with Section 14.01(a)(xvi) of the Original Indenture, the Company wishes to increase the aggregate principal amount of Bonds which may be authenticated and delivered under the Indenture to One Billion Dollars ($1,000,000,000), effective upon the filing for record of this Nineteenth Supplemental Indenture in all counties in which the Mortgaged Property, as defined in Section 1.01 of the Indenture, is located; and

WHEREAS, the Company, in the exercise of the powers and authority conferred upon and reserved to it under the provisions of the Indenture, and pursuant to appropriate resolutions of the Board of Directors, has duly resolved and determined to make, execute and deliver to the Trustee a Supplemental Indenture in the form hereof for the purposes herein provided; and

WHEREAS, all conditions and requirements necessary to make this Supplemental Indenture a valid, binding and legal instrument have been done, performed and fulfilled and the execution and delivery hereof have been in all respects duly authorized;

THAT the Company, in consideration of the acceptance or the purchase and ownership (as applicable) from time to time of the bonds issued under the Indenture and the service by the Trustee and its successors, under the Indenture and of One Dollar to it, duly paid by the Trustee at or before the ensealing and delivery of these presents, the receipt whereof is hereby acknowledged, hereby covenants and agrees to and with the Trustee and its successors in the trust under the Indenture, for the benefit of those who shall hold the Bonds as follows:

The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or the due execution hereof by the Company or for or in respect of the recitals contained herein, all of which recitals are made by the Company solely. In general, each and every term and condition contained in Article Eleven of the Indenture shall apply to this Supplemental Indenture with the same force and effect as if the same were herein set forth in full, with such omissions, variations and modifications thereof as may be appropriate to make the same conform to this Supplemental Indenture.

IN WITNESS WHEREOF, said NorthWestern Corporation has caused this Supplemental Indenture to be executed on its behalf by an Authorized Executive Officer as defined in the Indenture; and The Bank of New York Mellon, in evidence of its acceptance of the trusts hereby created, has caused this Supplemental Indenture to be executed on its behalf by one of its Vice Presidents; all as of the 1st day of June, 2023.

                        NORTHWESTERN CORPORATION

                        By /s/ Crystal D. Lail             

                         Crystal D. Lail

                         Vice President and Chief Financial Officer

                            THE BANK OF NEW YORK MELLON

                            By /s/ Stacey B. Poindexter             

                            Name: Stacey B. Poindexter

                            Title: Vice President

STATE OF SOUTH DAKOTA    )

                    )SS.

COUNTY OF     LINCOLN        )

(NOTARIAL SEAL)                     /s/ Chelsey Wilson             

                            Notary Public

STATE OF NEW YORK         )

                    )SS.

COUNTY OF    NEW YORK        )

(NOTARIAL SEAL)                     /s/ Edward Cofie             

                            Notary Public

    The following properties, located in the following counties of the State of South Dakota, are subject to the Lien of the Indenture pursuant to Granting Clause Second of the Original Indenture:

None.