Mont. Code § 7-2-4625
An incorporated city or town may create an annexation district outside of the city or town. Territory may be included in an annexation district only upon an agreement between the city or town and the owner of the property included in a district. The agreement may specify the duration of the district, which may not exceed 10 years. A city or town may provide the services specified in the agreement between the city or town and the property owner to the property in the district. The city or town may impose a tax levy or a fee on the owner of the property within the annexation district based upon the difference between the municipal levy or fee and the nonmunicipal levy or fee. By the end of the period specified in the agreement, the levy or fee must be the full amount that a resident of the city or town would pay in the year that the property is annexed. Unless the agreement provides otherwise, the property in the district is annexed after the period specified in the agreement, and the district is dissolved. A delinquency in a payment by the owner of property in the annexation district is collectible in the same manner that other delinquent taxes or fees are collectible.
§ 7-2-4625, MCA