Whenever territory adjoining any incorporated city or town is surveyed and laid off into streets or blocks as an addition thereto, said territory may become a part of such city or town: (1) upon filing the map or plat thereof in the office of the county clerk; and (2) upon the approval of the mayor and a majority of the council endorsed thereon.
Additions To Municipalities
Mont. Code Ann. § 7-2-4201, under Addition to Municipalities.
Mont. Code Ann. § 7-2-4201