Coffee Creek

Fergus County (Lewistown county seat; central Montana; ~11,500 residents; bounded south by the Big Snowy / Little Snowy / Judith Mountains; spans into the Charles M. Russell National Wildlife Refuge / Missouri River Breaks to the north) does not maintain a comprehensive countywide zoning code. Like most rural central-Montana counties, Fergus operates under Montana's permissive default: parcels in unincorporated territory have no county-imposed zoning unless a specific zoning district has been formally created under MCA Title 76, Chapter 2 Part 1 (county zoning) or Part 2 (planning-and-zoning districts). Montana SB 528 (MCA § 76-2-345) preempts MUNICIPAL ADU zoning to require ADUs by-right inside city limits — but only Lewistown (population ~5,800) clearly clears the SB 323 5,000-resident duplex-preemption threshold. SB 528 ADU preemption applies to all incorporated cities regardless of size, including Lewistown, Denton, Grass Range, Moore, and Winifred. For unincorporated parcels — the bulk of the county by area — the only land-use constraints are typically subdivision review under the Montana Subdivision and Platting Act, on-site sewage rules under MCA Title 75 Ch. 5, and any voluntary covenants on the parcel. An ADU on an unincorporated Fergus County parcel is generally permissible without county zoning approval, subject to building-code compliance and septic permitting through the local sanitarian. The Charles M. Russell National Wildlife Refuge (CMR) covers ~1.1 million acres along the Missouri River in northern Fergus County and adjacent counties (Petroleum, Phillips, Valley, McCone, Garfield); private inholdings within the CMR are rare but can carry refuge-coordination requirements for new construction.

State-floor overlay: Montana SB 528 (MCA § 76-2-345) establishes a state floor for ADU permissibility in incorporated cities; the county's lack of a comprehensive zoning code in unincorporated territory means ADUs face no county zoning bar there.

Fergus County's overlay footprint is shaped by three distinct geographies: (1) the Lewistown-area FEMA NFIP floodplain along Big Spring Creek and the Judith River (relatively narrow but covers downtown Lewistown reaches), (2) the WUI footprint of the Big Snowy / Little Snowy / Judith Mountains (forested parcels at elevation), and (3) the Charles M. Russell National Wildlife Refuge boundary along the Missouri River — a federal overlay with refuge-coordination implications for any private inholding (rare) or for new development on adjacent parcels. No coastal or seismic overlays. Lewistown has a NRHP commercial historic district downtown.

• FEMA NFIP Special Flood Hazard Areas - Big Spring Creek, Judith River, Missouri River — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; elevation cost can add $15,000-$40,000.
• Wildland-Urban Interface - Big Snowy, Little Snowy, Judith Mountains — Voluntary defensible space and ignition-resistant construction recommended; not formally required by county code.
• Charles M. Russell National Wildlife Refuge — Refuge boundaries are mapped on USFWS GIS. Most Fergus County residential parcels are far enough south of the refuge that this overlay is not material; the relevance is concentrated in the Hilger / Roy / Winifred area approaching the refuge.
• Lewistown Central Business District (NRHP) — ADU work on a NRHP-listed contributing property triggers Section 106 review only if federal financing or permitting (FHA, USDA RD, HUD-184) is involved.

Fergus County does not operate a county building department in the traditional sense. For unincorporated parcels, building permits are generally not required by the county for residential construction outside any formally-created zoning district. The state-adopted Montana Building Code applies as a technical floor; enforcement in counties without a building department falls back to the State Building Codes Bureau on complaint or to point-of-sale inspection requirements. The single permit most likely to be required is the on-site wastewater (septic) permit issued by the County Sanitarian / Public Health Department under MCA Title 75 Ch. 5 and ARM Title 17 Ch. 36. Subdivision review by the County Planning Office applies if creating a new parcel; placing an ADU on an existing parcel does not normally trigger subdivision review. Lewistown city (the only meaningful population concentration) operates its own building permits inside city limits.