RE: $90,000,000 6.63% SENIOR NOTES

Exhibit 4.1

EXECUTION COPY

Otter Tail Corporation

Fourth Amendment
Dated as of June 30, 2009

to

Note Purchase Agreement
Dated As Of December 1, 2001

Re: $90,000,000 6.63% Senior Notes
Due December 1, 2011

Fourth Amendment To Note Purchase Agreement

      This Fourth Amendment dated as of June 30, 2009 (the or this “ Fourth Amendment ”) to the Note Purchase Agreement dated as of December 1, 2001 is between and among Otter Tail Corporation , a Minnesota corporation (the “ Company ”), and each of the institutions which is a signatory to this Fourth Amendment (collectively, the “ Noteholders ”).

Recitals:

     A. The Company and each of the Purchasers signatory thereto have heretofore entered into the Note Purchase Agreement dated as of December 1, 2001, as amended by a First Amendment thereto dated as of December 1, 2002, by a Second Amendment thereto dated as of October 1, 2004 and by a Third Amendment thereto dated as of December 1, 2007 (as heretofore so amended, the “ Note Purchase Agreement ”). The Company has heretofore issued the $90,000,000 6.63% Senior Notes due December 1, 2011 (the “ Notes ”) dated December 27, 2001 pursuant to the Note Purchase Agreement.

     B. The Company has announced that it intends to restructure the Company into a holding company with Otter Tail Power Company as a separate, first-tier subsidiary (the “ Reorganization ”). The Company (“ Old Otter Tail ”) will form a direct, wholly owned subsidiary that will be a Minnesota corporation (“ New Otter Tail ”). New Otter Tail will form a direct, wholly owned subsidiary that will be a Minnesota corporation (“ Merger Sub ”). Old Otter Tail will transfer to New Otter Tail by way of assignment or contribution to capital all of the shares of capital stock of its direct, wholly owned subsidiaries. Pursuant to articles of merger and a plan of merger among Old Otter Tail, New Otter Tail and Merger Sub, Old Otter Tail will merge with Merger Sub (the “ Merger ”). The surviving corporation in the Merger will be Old Otter Tail and will have the name Otter Tail Power Company, and the current shareholders of Old Otter Tail will become shareholders of New Otter Tail. Immediately upon effectiveness of the Merger, New Otter Tail will change its name to Otter Tail Corporation. Immediately prior to the Merger, Old Otter Tail will transfer to New Otter Tail by way of assignment, and New Otter Tail will assume, all of the property, contracts, leases, rights, privileges, franchises, patents, trademarks, licenses, registrations and other assets and liabilities that pertain to the operation of the new holding company and that are not specific to the operation of the power company. Following the Merger, Otter Tail Power Company will be the holder of all of the rights and obligations of Old Otter Tail under the Note Purchase Agreement.

     C. The Company has requested, in connection with the Reorganization, that the Note Purchase Agreement be amended as set forth herein.

     D. The Company and the Noteholders now desire to amend the Note Purchase Agreement in the respects, but only in the respects, hereinafter set forth.

     E. Capitalized terms used herein shall have the respective meanings ascribed thereto in the Note Purchase Agreement (as amended hereby) unless herein defined or the context shall otherwise require.

     NOW, THEREFORE, upon the full and complete satisfaction of the conditions precedent to the effectiveness of this Fourth Amendment set forth in §2.1 hereof, and in consideration of

good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the Company and the Noteholders do hereby agree as follows:

SECTION 1. Amendments.

      Section 1.1. Section 8.7 of the Note Purchase Agreement is hereby amended by amending the definitions of “ Called Principal ,” “ Remaining Scheduled Payments ” and “ Settlement Date ” in their entirety to read as follows:

     “ Called Principal ” means, with respect to any Note, the principal of such Note that is to be prepaid pursuant to Section 8.2 or Section 22.8(d), is to be purchased pursuant to Section 8.3 or has become or is declared to be immediately due and payable pursuant to Section 12.1, as the context requires.

     “ Remaining Scheduled Payments ” means, with respect to the Called Principal of any Note, all payments of such Called Principal and interest thereon that would be due after the Settlement Date with respect to such Called Principal if no payment of such Called Principal were made prior to its scheduled due date, provided that if such Settlement Date is not a date on which interest payments are due to be made under the terms of the Notes, then the amount of the next succeeding scheduled interest payment will be reduced by the amount of interest accrued to such Settlement Date and required to be paid on such Settlement Date pursuant to Sections 8.2, 8.3, 12.1 or 22.8(d).

     “ Settlement Date ” means, with respect to the Called Principal of any Note, the date on which such Called Principal is to be prepaid pursuant to Section 8.2 or Section 22.8(d) or has become or is declared to be immediately due and payable pursuant to Section 12.1, as the context requires and with respect to the purchase of Notes pursuant to Section 8.3, the date on which the Notes are required thereunder to be purchased by the Company.

      Section 1.2. Effective as of the consummation of the Corporate Reorganization, Sections 9.8, 9.9, 9.10, 9.11 and 9.12 of the Note Purchase Agreement shall be deleted in their entirety.

      Section 1.3. Section 10.3 of the Note Purchase Agreement is hereby amended in its entirety to read as follows:

     “Section 10.3 Limitation on Liens . The Company will not, and will not permit any Subsidiary to, directly or indirectly create, incur, assume or permit to exist (upon the happening of a contingency or otherwise) any Lien on or with respect to any property or asset (including, without limitation, any document or instrument in respect of goods or accounts receivable) of the Company or any such Subsidiary, whether now owned or held or hereafter acquired, or any income or profits therefrom, or assign or otherwise convey any right to receive income or profits, except:

     (a) Liens for taxes and assessments or governmental charges or levies and Liens securing claims or demands of mechanics and materialmen; provided that payment thereof is not at the time required by Section 9.4;

     (b) Liens of or resulting from any judgment or award in an aggregate amount not to exceed $10,000,000, the time for the appeal or petition for rehearing of which shall not have expired, or in respect of which the Company or a Subsidiary shall at any time in good faith be prosecuting an appeal or proceeding for a review and in respect of which a stay of execution pending such appeal or proceeding for review shall have been secured;

     (c) Liens incidental to the conduct of business or the ownership of properties and assets (including, without limitation, Liens in connection with worker’s compensation, unemployment insurance and other like laws, carrier’s, warehousemen’s liens and statutory landlords’ liens) and Liens to secure the performance of bids, tenders or trade contracts, or to secure statutory obligations, surety or appeal bonds or other Liens of like general nature, in any such case incurred in the ordinary course of business and not in connection with the borrowing of money; provided in each case, the obligation secured is not overdue or, if overdue, is being contested in good faith by appropriate actions or proceedings;

     (d) minor survey exceptions or minor encumbrances, easements or reservations, or rights of others for rights-of-way, utilities and other similar purposes, or zoning or other restrictions as to the use of real properties, which are reasonably necessary for the conduct of the activities of the Company and its Subsidiaries or which customarily exist on properties of corporations engaged in similar activities and similarly situated and which do not in any event materially impair their use in the operation of the business of the Company and its Subsidiaries;

     (e) Liens securing Debt of a Subsidiary to the Company or to a Wholly-Owned Subsidiary;

     (f) Liens existing as of December 1, 2001 and described on Schedule 5.15 hereto and Liens securing any refinancing of Indebtedness secured by such Liens, provided that such refinancing shall be subject to similar terms and secured by the same assets and the principal amount of Indebtedness secured thereby is not increased;

     (g) Liens in connection with the acquisition of property after the date hereof by way of purchase money mortgage, conditional sale or other title retention agreement, Capital Lease or other deferred payment contract, provided that such Liens attach only to the property being acquired and that the Debt secured thereby does not exceed the Fair Market Value of such property at the time of acquisition thereof and the Lien shall be created contemporaneously with, or within 180 days after, the acquisition of such property;

     (h) Liens that existed on assets of other Persons at the time of acquisition of such other Persons or of such assets by the Company or a Subsidiary and which continue to attach only to such assets and Liens securing any refinancing of Indebtedness secured by such Liens, provided that such refinancing shall be subject to similar terms and secured by the same assets and the principal amount of Indebtedness secured thereby is not increased;

     (i) Liens (to the extent falling under the definition of “Lien”) consisting of ownership interests (and protective filings respecting such ownership interests) of lessors of assets (other than Utility Assets) to the Company or any Subsidiary under any operating lease, and of licensors of intellectual property or other rights to the Company or any Subsidiary; it being understood and agreed that for purposes of this clause (i), rail cars shall not be considered Utility Assets;

     (j) Liens (to the extent falling under the definition of “Lien”) consisting of rights of lessees or sublessees of certain owned real estate of the Company or any Subsidiary leased in the ordinary course of the Company’s or such Subsidiary’s business, which leases do not materially interfere with the ordinary course of business of the Company or such Subsidiary;

     (k) Liens arising under or related to any statutory or common law provisions, or customary account agreements, relating to banker’s liens or rights of setoff (but in no event including any grant of a security interest) as to deposit or securities accounts or other funds or instruments maintained or held with a depositary or other financial institution or securities intermediary;

     (l) Liens created, assumed or incurred after the date of the Closing given to secure Debt of the Company or any Subsidiary in addition to the Liens permitted by the preceding clauses (a) through (k) hereof; provided that all Debt secured by Liens permitted under this Section 10.3(l) does not exceed $2,000,000 in the aggregate at any time outstanding and in no event shall any Lien permitted by this Section 10.3(l) secure any obligation under the Bank Credit Agreement or any related document;

provided that (1) all Debt secured by such Liens shall have been incurred within the applicable limitations provided in Section 10.1(b) and (2) at the time of creation, assumption or incurrence of the Debt secured by such Lien and after giving effect thereto and to the application of the proceeds thereof, no Default or Event of Default would exist.”

      Section 1.4. Effective as of the consummation of the Corporate Reorganization, Section 10.7 of the Note Purchase Agreement is hereby amended in its entirety to read as follows:

     “ Section 10.7 Benefit of More Restrictive Covenants or More Favorable Terms. If any Lender under the Bank Credit Agreement, or if any 2007 Noteholder under the 2007 Note Purchase Agreement, is or becomes entitled to

the benefit of any (i) covenant, (ii) agreement, (iii) event of default, or (iv) other event which would permit the Lender or the 2007 Noteholder, as the case may be, to have the Company Debt obligations it holds purchased by the Company (a “ put event ”), which is more restrictive on the Company or its Subsidiaries than the covenants, agreements, events of default or put events contained herein or which is more favorable to such Lender or such 2007 Noteholder, as the case may be, than the covenants, agreements, events of default or put events contained herein, then such more restrictive or more favorable covenant, agreement, event of default or put event shall be deemed to be incorporated into this Agreement by reference during any period such Lender or 2007 Noteholder is so entitled thereto without regard to any waivers by some or all of the Lenders or some or all of the 2007 Noteholders, as the case may be, with respect thereto and shall remain so incorporated for a period of 30 days after the Lender or the 2007 Noteholder, as the case may be, is no longer entitled to the benefit thereof and the Noteholders shall be entitled to the benefits thereof with respect to this Agreement in addition to the existing covenants, agreements, events of default and put events contained herein so long as any of the Notes remain outstanding.

     Prior to any closing of the effectuation of any amendment or modification to the Bank Credit Agreement or the 2007 Note Purchase Agreement, the Company shall deliver a letter to the Noteholders containing a list of those covenants, agreements, events of default and put events which are deemed to be incorporated into this Agreement pursuant to the foregoing provisions of this Section 10.7 and concurrently with or prior to the execution of any amendment to the Bank Credit Agreement or the 2007 Note Purchase Agreement, the Company shall deliver to the Noteholders a letter setting forth all covenants, agreements, events of default and put events and/or changes thereto which are deemed to be incorporated into this Agreement pursuant to the foregoing provisions of this Section 10.7 and any such letters delivered to the Noteholders shall be satisfactory in form and substance to the Noteholders. At any time after the receipt of any such letter the Required Holders shall have the right by delivery of written notice to the Company to amend this Agreement by adding to this Agreement any covenants, agreements, events of default or put events referred to in any such letter which the Required Holders elect to add pursuant to the foregoing provisions of this Section 10.7.”

      Section 1.5. Clauses (i), (j) and (k) of Section 10.10 of the Note Purchase Agreement are hereby amended in their entirety to read as follows:

     “(i) prior to consummation of the Corporate Reorganization, (i) Investments outstanding on April 30, 2002 in Subsidiaries by the Company and other Subsidiaries, and (ii) Investments by the Company or Subsidiaries in Persons that will be Subsidiaries upon completion of such Investments;

     (j) upon and subsequent to consummation of the Corporate Reorganization, equity Investments by the Company or any Subsidiary in a Person that conducts only a Regulated Business or a business that is solely the

generation, transmission, distribution or sale of electricity in the United States, which Person will be a Subsidiary upon completion of such Investment; provided, that upon the making of such Investment such Person will execute a guaranty agreement in respect of the Notes in form, scope and substance satisfactory to the Required Holders and, if then or at any time thereafter such Person creates, incurs, assumes or otherwise becomes liable with respect to any Debt (including, without limitation, Debt in the form of a Guaranty) other than Debt represented by such guaranty agreement in respect of the Notes, such Person shall cause the holder or obligee with respect to such other Debt to enter into an intercreditor agreement in form, scope and substance satisfactory to the Required Holders; and

     (k) (i) Investments by any Material Subsidiary constituting loans to the Company and (ii) provided that no Default or Event of Default shall have occurred and be continuing, Investments made by the Company or any Material Subsidiary constituting loans to (A) any Material Subsidiary or (B) any Subsidiary that is not a Material Subsidiary, provided that such loans under the foregoing clauses (A) and (B) to any one Subsidiary shall not exceed $15,000,000 in aggregate principal amount outstanding at any time, and provided, further, that after the Corporate Reorganization, the only loans under the foregoing clauses (A) and (B) that will be permitted to be acquired for value, made, had, held or permitted to remain outstanding shall be those made to Subsidiaries that conduct only a Regulated Business.”

      Section 1.6. Section 10.11 of the Note Purchase Agreement is hereby amended in its entirety to read as follows:

     “Section 10.11 Contingent Liabilities . The Company will not and will not permit any Material Subsidiary to either: (a) endorse, guarantee, contingently agree to purchase or to provide funds for the payment of, or otherwise become contingently liable upon, any obligation of any other Person, except by the endorsement of negotiable instruments for deposit or collection (or similar transactions) in the ordinary course of business, or (b) agree to maintain the net worth or working capital of, or provide funds to satisfy any other financial test applicable to, any other Person, except (in the case of (a) or (b) above) for:

     (i) guaranties by the Company of loans to leveraged Employee Stock Ownership Plans;

     (ii) prior to consummation of the Corporate Reorganization, guaranties by Varistar Corporation of obligations of DMI Industries, Inc. in respect of down payments by customers of DMI Industries, Inc. in aggregate amounts of up to $30,000,000, with the amount of such guaranties to be deemed to be either (x) the dollar limitation set forth in any such guaranty, if applicable, or (y) the amount of such down payment so guaranteed;

     (iii) guaranties by the Company or any Material Subsidiary of obligations of any Material Subsidiary as lessee under any lease that is not a Capital Lease;

     (iv) other guaranties limited as to principal of recovery to not more than $10,000,000 in the aggregate, provided that no such guaranty shall relate to any obligation under the Bank Credit Agreement or any related document;

     (v) prior to consummation of the Corporate Reorganization, guaranties by Material Subsidiaries of the obligations of Varistar Corporation under the Amended and Restated Credit Agreement, dated as of December 23, 2008, among Varistar Corporation, the lenders party thereto and U.S. Bank National Association, as agent (the “ Varistar Credit Agreement ”); and

     (vi) prior to consummation of the Corporate Reorganization, guaranties by Material Subsidiaries of obligations of the Company under the Cascade Note so long as each and every Subsidiary that guarantees the obligations of the Company under the Cascade Note is a Subsidiary Guarantor or an Additional Subsidiary Guarantor or becomes an Additional Subsidiary Guarantor in accordance with the terms of Section 9.8 hereof.”

      Section 1.7. Section 11 of the Note Purchase Agreement is hereby amended in its entirety to read as follows:

     “An “Event of Default” shall exist if any of the following conditions or events shall occur and be continuing:

     (a) the Company defaults in the payment of any principal or Make-Whole Amount, if any, on any Note when the same becomes due and payable, whether at maturity or at a date fixed for prepayment or by declaration or otherwise; or

     (b) the Company defaults in the payment of any interest on any Note for more than five Business Days after the same becomes due and payable; or

     (c) the Company defaults (i) in the performance of or compliance with any term contained in Section 10 or Section 7.1(d) or (ii) in the payment when due of the amount required to be paid by the Company for the purchase of any Note pursuant to Section 8.3; or

     (d) the Company defaults in the performance of or compliance with any term contained herein (other than those referred to in paragraphs (a), (b) and (c) of this Section 11) and such default is not remedied within 30 days after the earlier of (i) a Responsible Officer obtaining actual knowledge of such default and (ii) the Company receiving written notice of such default from any holder of a Note (any such written notice to be

identified as a “notice of default” and to refer specifically to this paragraph (d) of Section 11); or

     (e) any representation or warranty made in writing by or on behalf of the Company or by any officer of the Company in this Agreement or in any writing furnished in connection with the transactions contemplated hereby proves to have been false or incorrect in any material respect on the date as of which made; or

     (f) (i) the Company or any Material Subsidiary is in default (as principal or as guarantor or other surety) in the payment of any principal of or premium or make-whole amount or interest on any Indebtedness that is outstanding in an aggregate principal amount of at least $10,000,000 beyond any period of grace provided with respect thereto, or (ii) the Company or any Material Subsidiary is in default in the performance of or compliance with any term of any evidence of any Indebtedness in an aggregate outstanding principal amount of at least $10,000,000 or of any mortgage, indenture or other agreement relating thereto or any other condition exists, and as a consequence of such default or condition such Indebtedness has become, or has been declared (or one or more Persons are entitled to declare such Indebtedness to be), due and payable before its stated maturity or before its regularly scheduled dates of payment; or

     (g) the Company or any Material Subsidiary (i) is generally not paying, or admits in writing its inability to pay, its debts as they become due, (ii) files, or consents by answer or otherwise to the filing against it of, a petition for relief or reorganization or arrangement or any other petition in bankruptcy, for liquidation or to take advantage of any bankruptcy, insolvency, reorganization, moratorium or other similar law of any jurisdiction, (iii) makes an assignment for the benefit of its creditors, (iv) consents to the appointment of a custodian, receiver, trustee or other officer with similar powers with respect to it or with respect to any substantial part of its property, (v) is adjudicated as insolvent or to be liquidated, or (vi) takes corporate action for the purpose of any of the foregoing; or

     (h) a court or governmental authority of competent jurisdiction enters an order appointing, without consent by the Company or any of its Material Subsidiaries, a custodian, receiver, trustee or other officer with similar powers with respect to it or with respect to any substantial part of its property, or constituting an order for relief or approving a petition for relief or reorganization or any other petition in bankruptcy or for liquidation or to take advantage of any bankruptcy or insolvency law of any jurisdiction, or ordering the dissolution, winding-up or liquidation of the Company or any of its Material Subsidiaries, or any such petition shall be filed against the Company or any of its Material Subsidiaries and such petition shall not be dismissed within 60 days; or

     (i) a final judgment or judgments for the payment of money aggregating in excess of $10,000,000 are rendered against one or more of the Company and its Material Subsidiaries and which judgments are not, within 30 days after entry thereof, bonded, discharged or stayed pending appeal, or are not discharged within 30 days after the expiration of such stay; or

     (j) prior to consummation of the Corporate Reorganization, default shall occur in the observance or performance of any provision of the Guaranty Agreement or the Guaranty Agreement shall cease to be in full force and effect for any reason except by operation of Section 9.12, including, without limitation, a final and nonappealable determination by any governmental body or court that the Guaranty Agreement is invalid, void or unenforceable, or any Subsidiary Guarantor or any Additional Subsidiary Guarantor shall contest or deny in writing the