ADU Pass
Liberty County
ADU Pass helps homeowners in Liberty County, Montana navigate the permit paperwork for building an accessory dwelling unit. We cover 5 cities and 5 ZIP codes in this county.
Map
County ADU details
County ADU ordinance
Liberty County (Chester county seat; north-central Montana on the Hi-Line; ~2,000 residents across 1,430 sq mi; one of Montana's smallest-population counties; dryland wheat farming dominates the economy; the BNSF Hi-Line mainline crosses the southern county along US-2; Lake Elwell - also known as Tiber Reservoir - sits on the Marias River in the southwestern county and is a major recreational fishery and Bureau of Reclamation impoundment; minimal county-side zoning) does not maintain a comprehensive countywide zoning code. Liberty County operates under the Montana Subdivision and Platting Act (MCA Title 76 Ch. 3) and state building code (IRC 2018, administered by the Montana Department of Labor & Industry, Building Codes Bureau). Incorporated municipalities include Chester (~860 residents, county seat); both Joplin and Whitlash are unincorporated CDPs along US-2 / MT-409. Chester is subject to Montana SB 528 (2023, Mont. Code Ann. § 76-2-345) ADU preemption inside its town limits. SB 528 applies to ALL incorporated Montana cities (NOT population-gated per the Montana AG interpretation underlying the MT-CW2 finding). At the COUNTY tier, SB 528 is municipal-only and does NOT reach unincorporated county land. The county's economic base is wheat farming with some cattle ranching; Tiber Reservoir tourism and BNSF rail-stop economics provide modest secondary income.
State-floor overlay: Montana SB 528 establishes a state ADU floor for incorporated Montana cities; Chester is squarely subject inside its town limits. SB 528 does NOT extend to unincorporated Liberty County. ADU permissibility on unincorporated parcels is determined by state-level oversight only (no county zoning).
Adopting body: Liberty County Board of Commissioners (no countywide zoning ordinance; subdivision review only)
County permitting (unincorporated parcels)
Liberty County issues no countywide building permits for residential construction in unincorporated areas. Like most rural Montana Hi-Line counties without a full county building department, building-code enforcement is delegated to the State of Montana (Department of Labor & Industry, Building Codes Bureau) only for certain commercial or state-jurisdiction projects. Single-family residences and ADUs in unincorporated Liberty County are typically constructed without municipal-style plan review. State-level oversight applies to on-site septic (DEQ Subdivision review for parcels created after 1973) and well construction (DNRC water rights). Floodplain development requires a permit through the county floodplain administrator under MCA Title 76 Ch. 5 - applicable along the Marias River and Lake Elwell shoreline. Tiber Dam / Lake Elwell is a Bureau of Reclamation facility - shoreline construction within Reclamation withdrawal lands requires federal coordination. Chester operates its own town permitting process inside town limits. Liberty County is in IECC climate zone 6B (Hi-Line plains; harsh winter winds; ground snow loads 30-50 psf typical). SB 528 is municipal-only at the county tier - it does NOT reach unincorporated county land.
Impact fees: Liberty County and Chester levy no impact fees. SB 528 prohibits ADU-specific impact fees in Chester; the town has no general residential impact-fee schedule.
County assessor
Property assessment in Montana is centralized at the Montana Department of Revenue (DOR), not the county. The Liberty County DOR field operations are administered through the Great Falls / Havre regional offices. ADU additions are captured as improvements to the host parcel on the next biennial residential reappraisal cycle - capture is delayed by the absence of a county building department feeding shared permit data. Mont. Code Ann. § 15-6-134 establishes Class 4 residential property and taxable-value calculation. MCA § 15-6-222 establishes a homestead exemption for principal residences. Montana operates on a two-year reappraisal cycle for residential property under MCA § 15-7-111. Liberty County's tax base is dominated by Class 3 agricultural assessment under MCA § 15-6-133 - dryland wheat comprises the bulk of taxable acreage. Residential value appreciation has been modest 2020-2024, lagging western Montana's recreational counties.
Assessment policy: Improvement value for an ADU is added to the parcel record on the next biennial revaluation. Without a county building department, capture relies on field discovery, satellite imagery, owner self-report, or town-permit feeds (Chester) - delays of 1-3 years are common. Montana applies a Class 4 residential rate (~1.35% of market value, adjusting per legislative session) to compute taxable value. Class 3 agricultural assessment applies to most county acreage and is unaffected by an ADU as long as the parcel retains agricultural use. Homestead / principal-residence treatment under MCA § 15-6-222 (and HB 231 2025 adjustments) shields the existing structure but new improvement value is fully captured. Appeals run first to the Liberty County Tax Appeal Board (CTAB) and then to the Montana Tax Appeal Board.
County overlays (4)
Liberty County's overlay landscape is light, reflecting the county's small population and prairie-dominated geography: (1) FEMA NFIP floodplain along the Marias River (the southwestern county spine, including Lake Elwell shoreline), Sage Creek, and Willow Creek. (2) Bureau of Reclamation withdrawal lands around Tiber Dam / Lake Elwell - federal lands with shoreline/access permitting through the Bureau of Reclamation Montana Area Office; this is the dominant federal overlay in Liberty County. (3) Wildland-Urban Interface is light (prairie geography with limited forest cover); grass-fire risk is the primary fire concern rather than forest-fire risk. (4) BNSF Railway Hi-Line mainline corridor through Joplin, Lothair, and Chester - rail-adjacent setbacks and noise considerations apply at the CDP cores. (5) NRHP-listed structures are scattered and modest - no major historic district overlay.
- FEMA NFIP Special Flood Hazard Areas - Marias River, Lake Elwell shoreline, Sage Creek, Willow Creek — Spring snowmelt and ice-jam events on the Marias drive flooding peaks. Lake Elwell / Tiber Reservoir levels are managed by Bureau of Reclamation - shoreline development outside the federal withdrawal lands but within the FEMA flood zone faces both county SFHA permits and Reclamation coordination. ADU elevation cost where applicable runs $10,000-$25,000 (lower than higher-density markets).
- Bureau of Reclamation withdrawal lands - Tiber Dam / Lake Elwell — Reclamation lease cabins on Lake Elwell exist under historical lease arrangements; new cabin/ADU additions are heavily constrained by Reclamation policy. Private inholdings adjacent to withdrawal lands (Tiber Ridge area, Sanford Park-adjacent private parcels) face access easement and shoreline-use coordination requirements. Lake Elwell walleye fishery drives sustained but modest STR demand on private adjacent parcels.
- Wildland-Urban Interface - prairie grass-fire exposure (limited forest WUI) — Insurance markets are stable for prairie parcels. Grass-fire risk is mitigated by tilled cropland providing defensible space around most farmsteads. Sweet Grass Hills foothills face moderate underwriter caution but the WUI exposure is modest compared to mountain counties.
- BNSF Railway Hi-Line mainline corridor — Rail-adjacent ADU economics in Hi-Line CDPs are constrained by noise; underwriting on rail-adjacent residential is conservative. Chester's downtown core is rail-adjacent - several blocks of older housing stock are within the immediate noise zone.
Known county issues (4)
- other — Permitting timelines in Liberty County are typically driven by clerk availability rather than substantive review burden. ADU project timelines are competitive on shoulder-season schedules; peak agricultural seasons (planting, harvest) can extend response times because county clerks may share staffing with elections / other peak-load functions.
- other — ADU rental yield in Liberty County is modest (~$700-$1,000/month for a one-bedroom rural rental, where rental market exists at all). Family-housing and farm-hand ADUs dominate. Lake Elwell shoreline-adjacent ADUs can capture seasonal STR premium during walleye season (May-October).
- other — ADU project cost in Liberty County runs $170-$220/sqft baseline. Wind-exposed Hi-Line plains parcels face additional envelope sealing and slab-edge frost protection cost. Operating cost (heating) is high. Construction labor must travel from Havre (~30 mi) or Great Falls (~100 mi) - logistics premium adds 5-10% versus equivalent metro construction.
- other — Lake Elwell shoreline ADU economics are constrained by federal jurisdiction on Reclamation parcels. Private adjacent parcels can capture walleye-fishery STR premium but require careful navigation of access easements. Pre-application coordination with Bureau of Reclamation Montana Area Office (Great Falls) is essential for any project within or adjacent to withdrawal lands.
Montana state — ADU law and programs
State ADU law
Montana has enacted strong statewide ADU preemption through Senate Bill 528 (2023), codified at Mont. Code Ann. § 76-2-345. SB 528 is part of the 2023 'Montana Miracle' housing reform package (also including SB 323 duplex preemption and SB 245 commercial-zone multifamily). SB 528 requires every Montana city to allow at least one ADU by right on any lot containing a single-family dwelling, with size capped at the lesser of 1,000 sq ft or the floor area of the primary dwelling. ADUs may be attached, detached, or internal. Cities are prohibited from requiring additional parking, fees, design-match to the primary dwelling, owner-occupancy, occupant-relationship limits, or impact fees specifically for ADUs. ADUs must still meet building, fire, and public-health codes. Effective 2024-01-01. The Montana Supreme Court (September 2024) lifted a Gallatin County district-court injunction obtained by Montanans Against Irresponsible Densification (MAID), allowing the law to take effect; a Daily Montanan March 2025 ruling confirmed the affordable-housing bills are a 'legitimate government concern.' The 2025 session continued the reform trajectory (HB 533 wildfire-insurance transparency); no rollback bills have advanced as of 2026-04-26.
State HOA preemption
Montana's HOA statute Mont. Code Ann. § 70-17-901 (https://mca.legmt.gov/bills/mca/title_0700/chapter_0170/part_0090/section_0010/0700-0170-0090-0010.html) prohibits an HOA from adopting or enforcing a covenant amendment that imposes more onerous use restrictions than those in place when a member acquired their interest, unless the affected member consents in writing. After 2019-05-09, an HOA also may not enforce a covenant in a way that limits uses that were allowed when the member acquired the property. This is a one-way ratchet protecting existing uses, not an affirmative ADU preemption: an HOA's pre-existing covenant prohibiting ADUs remains enforceable against owners who took title with that restriction in place. SB 528's text expressly addresses municipal zoning, not private covenants, and § 70-17-901(2) carves out covenants required to comply with applicable federal, state, and local laws — but a covenant banning ADUs is not 'required' by SB 528, so the carve-out does not flip pre-existing ADU bans. A homeowner subject to an HOA covenant prohibiting ADUs has no state-law remedy under current Montana law and must seek the consent or amendment process within the association.
State financing programs
Montana Board of Housing (MBOH) under the Montana Department of Commerce does not operate an ADU-specific loan or grant product as of 2026-04-26. Construction or rehab of an ADU on a primary residence may be financed indirectly through MBOH's Regular Bond Loan Program (30-year, low-interest first mortgage geared to first-time buyers under income and purchase-price limits) or the Bond Advantage / MBOH Plus Down Payment Assistance Programs (up to 5% / $15,000 in DPA). All MBOH first-mortgage products require qualifying for an underlying FHA, VA, RD, or HUD-184 loan; an existing ADU on the property is generally permissible. The Department of Commerce's Coal Trust Multifamily Loan Program funds rental housing developments which can include ADU-style units in multi-unit projects but is not a homeowner-facing instrument.
State housing programs
Montana does not operate a statewide pre-approved ADU plan catalog as of 2026-04-26. The 2023 Montana Miracle reform package (SB 528, SB 323, SB 245, SB 382) established the country's most aggressive state preemption of single-family-only zoning, but did not pair the preemption with a state plan library, impact-fee waiver fund, or per-ADU rebate. SB 382 (the Montana Land Use Planning Act, https://archive.legmt.gov/bills/2023/BillPdf/SB0382.pdf) restructures comprehensive-planning requirements for cities of 5,000+ residents toward a more streamlined, plan-then-permit model. Implementation by the Department of Commerce and the Department of Environmental Quality continues; the DEQ Energy Code office published an ADU best-practices guide in fall 2023.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.