Mont. Code Ann. § 7-4-4306

The mayor has power to exercise the power as may be vested in the mayor by ordinance of the city or town, in and over all places within 5 miles of the boundaries of the city or town for the purpose of enforcing the health and quarantine ordinances and regulations of the city or town. The board of county commissioners of the county affected by the ordinance and the local health board, if a local health board exists in the area affected by the ordinance, shall approve the ordinance by a majority vote.