(1) A person who sells the goodwill of a business may agree with the buyer to refrain from carrying on a similar business within the areas provided in subsection (2) so long as the buyer or any person deriving title to the goodwill from the buyer carries on a like business in the described areas.

(2) The agreement authorized in subsection (1) may apply in:

(a) the city where the principal office of the business is located;

(b) the county where the principal office of the business is located;

(c) a city in any county adjacent to the county in which the principal office of the business is located;

(d) any county adjacent to the county in which the principal office of the business is located; or

(e) any combination of the areas in subsections (2)(a) through (2)(d).

See https://leg.mt.gov/bills/mca/title_0280/chapter_0020/part_0070/sections_index.html