Mont. Code Ann. § 67-10-406

Any property in this state acquired by a municipality for airport purposes pursuant to the provisions of this chapter and any income derived by such municipality from the ownership, operation, or control thereof is exempt from taxation to the same extent as other property used for public purposes. Any municipality is authorized to exempt from municipal taxation any property acquired within its boundaries by a public agency of another state for airport purposes and any income derived from such property to the extent that such other states authorize similar exemptions from taxation to municipalities of this state.