Mont. Code Ann. § 7-14-1137

Any property in this state acquired by an authority for port purposes pursuant to the provisions of this part, any income derived by the authority from the ownership, operation, or control thereof, including property acquired, and income derived from organizations, including corporations organized under Title 32, chapter 4, whose purpose is to advance the economic development of its jurisdiction and of the state and its citizens, are exempt from taxation to the same extent as other property used for public purposes.