Mont. Code Ann. § 76-2-903

A city, county, taxing district, or other political subdivision of this state may not adopt an ordinance or resolution that prohibits any existing agricultural activities or forces the termination of any existing agricultural activities outside the boundaries of an incorporated city or town. Zoning and nuisance ordinances may not prohibit agricultural activities that were established outside the corporate limits of a municipality and then incorporated into that municipality by annexation.