Mont. Code Ann. § 76-4-103

The plat for a subdivision must show all parcels, whether contiguous or not. A parcel that is 20 acres or more in size, exclusive of public roadways, is not subject to review under this part unless the parcel provides two or more permanent spaces for recreational camping vehicles or mobile homes. The rental or lease of one or more parts of a single building, structure, or other improvement, whether existing or proposed, is not a subdivision, as that term is defined in this part, and is not subject to the requirements of this part.