Montana Subdivision review: what it allows on a lot
Subdivision review is Montana law, and the official source is at leg.mt.gov.
Splitting land usually needs county review under the Montana Subdivision and Platting Act.
Whether it applies to one lot turns on where the lot is and what it is zoned; the city, county or state office named in the law decides. Mapped areas are approximate. This is a plain reading of public law with its source, not legal advice.
Free, no account. ParcelSheet shows the lot's mapped size, parcel lines and flood zone, and this law on the lot's Montana sheet.
Other Montana laws on a lot: 2023 housing laws, Water rights.