EXHIBIT 5.1



              [LETTERHEAD OF PAUL, HASTINGS, JANOFSKY & WALKER LLP]

                                April 24, 2002


NorthWestern Corporation
125 S. Dakota Avenue
Sioux Falls, South Dakota  57104


Ladies and Gentlemen:

         We have acted as counsel to NorthWestern Corporation, a Delaware
corporation (the "Company"), in connection with the preparation and filing with
the Securities and Exchange Commission (the "Commission") of the Registration
Statement on Form S-4 (the "Registration Statement") of the Company for the
registration under the Securities Act of 1933, as amended (the "Securities
Act"), of $250,000,000 aggregate principal amount of the Company's 7-7/8% Senior
Notes due March 15, 2007 (the "New 2007 Notes") and $470,000,000 aggregate
principal amount of the Company's 8-3/4% Senior Notes due March 15, 2012 (the
"New 2012 Notes" and, together with the New 2007 Notes, the "New Notes"), to be
issued in exchange for a like principal amount of the Company's issued and
outstanding 7-7/8% Senior Notes due March 15, 2007 (the "Original 2007 Notes")
and 8-3/4% Senior Notes due March 15, 2012 (the "Original 2012 Notes" and,
together with the Original 2007 Notes, the "Original Notes"), respectively.

         In rendering this opinion, we have examined originals or copies,
certified or otherwise identified to our satisfaction, of the Registration
Statement, the Purchase Agreement, dated as of March 8, 2002 (the "Purchase
Agreement"), among the Company and the initial purchasers named in Schedule A
thereto (the "Purchasers"); the Registration Rights Agreement, dated as of March
13, 2002, among the Company and the Purchasers for the benefit of the Purchasers
and the holders of the Original Notes; the Indenture, dated as of November 1,
1998 (the "Base Indenture"), between the Company and JPMorgan Chase Bank, as
successor to The Chase Manhattan Bank, N.A., as trustee (the "Trustee"); the
Second Supplemental Indenture, dated as of March 13, 2002 (the "Second
Supplemental Indenture" and, together with the Base Indenture, the "Indenture"),
between the Company and the Trustee; the form of the New Notes; the Restated
Certificate of Incorporation of the Company, filed in the office of the
Secretary of State of the State of Delaware on November 9, 2000; the By-Laws of
the Company, as amended to February 7, 2001; and such other corporate records,
agreements, documents and other instruments, and such certificates or comparable
documents of public officials and of officers and representatives of the
Company, and have made such inquiries of such officers and representatives, as
we have deemed relevant and necessary as a basis for the opinion hereinafter set
forth.

                  In such examination, we have assumed the genuiness of all
signatures, the legal capacity of all natural persons, the authenticity and
completeness of all documents, certificates and instruments submitted to us as
originals, the conformity with the originals of all documents, certificates and
instruments submitted to us as certified, conformed or photostatic copies and
the authenticity and completeness of such latter documents, certificates and
instruments. As to all questions of fact relevant or material to this opinion,
we have relied without independent investigation on, and assumed the accuracy
and completeness of, certificates or comparable documents of officers and



representatives of the Company and upon the representations and warranties of
the Company contained in the Purchase Agreement. We have not made an
investigation as to, and have not independently verified, the facts underlying
the matters covered by the certificates or the Purchase Agreement.

         Based upon and subject to the assumptions, exceptions, qualifications
and limitations set forth herein, we are of the opinion that:

         1. The New Notes have been duly authorized by the Company and (assuming
the due authorization thereof by the Trustee) when duly executed and delivered
by the Company, authenticated by the Trustee in accordance with the terms of the
Indenture and delivered by the Company as contemplated by the Registration
Statement in exchange for Original Notes, will constitute the legal, valid and
binding obligations of the Company, enforceable against it in accordance with
their terms, subject to applicable bankruptcy, insolvency, reorganization,
fraudulent conveyance and transfer, moratorium and similar laws affecting
creditors' rights and remedies generally, and subject, as to enforceability, to
general principles of equity, including principles of commercial reasonableness,
good faith and fair dealing (regardless of whether enforcement is sought in a
proceeding at law or in equity).

         We are members of the Bar of the State of New York and our opinion
herein is limited to the laws of the State of New York, the General Corporation
Law of the State of Delaware and the federal laws of the United States, and we
do not express any opinion as to the laws of any other state or jurisdiction. We
consent to the use of this opinion as an exhibit to the Registration Statement
and to the reference to our firm under the caption "Legal Matters" in the
Prospectus which is a part of the Registration Statement. In giving this
consent, we do not hereby admit that we are within the category of persons whose
consent is required under Section 7 of the Securities Act and the rules and
regulations thereunder.

                                       Very truly yours,


                                       /s/ Paul, Hastings, Janofsky & Walker LLP