Mont. Code Ann. § 76-1-505

76-1-505 . Extension of boundaries of city-county planning board jurisdictional area. (1) The boundaries of the jurisdictional area can be extended further than 4 1/2 miles from the limits of the cities only upon petition signed by 5% or more of the resident freeholders living in excess of 4 1/2 miles and not more than 12 miles from the limits of the cities and within the area desiring to be included within said jurisdictional limits and upon presentation of said petition to the board of county commissioners.

(2) Thereafter, the board of county commissioners must by resolution set the proposed boundaries of said area and give notice of their intent to add said area to the jurisdictional limits theretofore created and of receipt of said petition by publication of notice of time and place of hearing on said petition and resolution. Said notice is to be published in a newspaper published in the county not less than 10 or more than 20 days prior to the date of said hearing. Thereafter, the boundaries of said area can only be set upon good cause being shown for the establishment of said extended jurisdictional area and the boundaries thereof, provided that such resolution shall not be adopted by the board of county commissioners if disapproved in writing by a majority of the freeholders of the territory proposed to be embraced. The jurisdictional area shall not extend more than 12 miles beyond the limits of any city within the jurisdictional area.