Mont. Code § 17-5-203
All bonds issued by any public body and all proceedings taken for the authorization and issuance of such bonds; for the levy, establishment, pledge, and appropriation of taxes, special assessments and other charges, and revenues to pay such bonds; and for the sale, exchange, execution, and delivery thereof, prior to the date set by and subject to the conditions set forth in 17-5-204, are validated, ratified, approved, and confirmed, notwithstanding any lack of power (other than constitutional) of such public body or the governing board or commission or officers thereof to authorize and issue such bonds or to sell, exchange, execute, or deliver the same and notwithstanding any defects or irregularities (other than constitutional) in such proceedings or in such sale, exchange, execution, or delivery, and bonds of such public bodies under the authority of such proceedings are binding, legal, valid, and enforceable obligations of such public body.
§ 17-5-203, MCA