Building permits, zoning and septic rules across Montana's counties

Montana has 37 of 56 counties without a residential building-permit requirement for unincorporated homes; city rules differ from these county counts¹. The highest-scoring counties in that group are Lewis and Clark County, Broadwater County, Mineral County, Lincoln County, Meagher County, Glacier County, Judith Basin County, Pondera County¹. Another 14 counties require residential building permits only in certain cases, and 5 require them⁶.

Use the Montana counties without building permits list to narrow the search, but a missing residential building permit does not remove separate electrical, plumbing or mechanical permit requirements^1,10. In state jurisdiction, farm and ranch buildings and residential buildings containing fewer than five dwelling units are exempt from state building permits, except residential buildings serving transient guests; certified local programs have their own requirements¹⁰. Qualifying owners have a contractor-license exemption, which does not waive applicable construction permits or inspections⁸.

Montana has 22 counties without countywide zoning, including Broadwater County, Mineral County, Sanders County, Judith Basin County, Pondera County, Beaverhead County, Teton County, Fergus County². Montana also has 25 counties with zoning⁶. The Montana no-zoning list is a starting point for comparing those county land-use answers².

For buyers seeking both conditions, 19 counties have neither a residential building-permit requirement nor countywide zoning; Broadwater and Mineral lead that group by Index score⁷. See the combined no-building-permit and no-countywide-zoning list for the full group⁷. Montana law allows county zoning for all or part of a jurisdictional area, with regulations that can differ between districts, so ask the county planning office whether the specific parcel lies in a zoning district¹¹. A county without countywide zoning still needs the separate drainfield and designated-floodplain checks described below^3,12.

Montana DEQ handles covered subdivision sanitation review, while the local health department issues the drainfield permit³. A Certificate of Subdivision Approval, commonly called a COSA, does not replace the drainfield permit needed to install a drainfield³. The county authority pattern lists 47 counties with county-issued septic permits, 7 served by a health district and 2 with state-agency permitting⁶. Because that pattern differs from DEQ's general description, confirm the actual drainfield office on the county page before applying^3,6.

DEQ's Subdivision Program reviews land divisions comprising less than 20 acres, plus condominiums and recreational camping vehicle and mobile home parks regardless of parcel size³. For a land purchase, request the existing COSA and ask the local health department whether the planned dwelling needs a new or changed drainfield permit³. DEQ's on-call engineer is the state contact for subdivision-review questions³.

Montana RV occupancy has county-level answers in 12 counties: 4 allow it as a county land-use matter and 8 impose conditions; the remaining 44 are unanswered, not automatically allowed or prohibited⁴. The allowed group is Fergus County, Musselshell County, Carter County, Petroleum County, with septic, floodplain and other applicable requirements still separate⁴. Compare the Montana RV-living county list before choosing a parcel⁴.

Tiny-home occupancy has answers in 14 counties: 10 allowed as a county land-use matter, 4 limited and 42 unanswered⁵. The highest-scoring allowed entries include Judith Basin County, Pondera County, Teton County, Fergus County, Musselshell County⁵. The Montana tiny-home list links the county-specific conditions⁵. Some limited RV answers concern rental spaces or RV parks, so ask the county planning office specifically about a personal RV on a private parcel⁴. DNRC's state-trust-land camping rule applies to recreation on state trust land and does not answer private-land residency¹³.

Lake County leads the Montana Index at 79, with limited residential building-permit requirements, zoning and county septic permitting; Gallatin County follows at 77 with the same authority pattern⁶. Lewis and Clark County also scores 77, with no residential building permit, zoning and county septic permitting⁶. Broadwater County and Mineral County each score 75, with no residential building permit or countywide zoning and county septic permitting⁶.

The next counties by score are Lincoln County at 74, with no residential building permit and zoning; Sanders County at 74, with limited residential building permits and no countywide zoning; and Meagher County at 73, with no residential building permit and zoning unconfirmed; all have county septic permitting⁶. Montana's median county farmland value is $1,283 per acre, a farmland benchmark rather than a specific homesite price⁶. The median county effective property-tax rate is 0.7%, and the median county property-tax bill is $1,719 annually⁶.

Montana follows prior appropriation, and 17 counties contain a special groundwater-management regime¹⁴. A new groundwater use of no more than 35 gallons per minute and 10 acre-feet annually may qualify for a permit exception, but eligibility is not automatic⁹. Combined appropriations from the same source exceeding 10 acre-feet require a permitted water right regardless of flow rate; multi-phase subdivision lots share the combined limit to qualify for the exception⁹.

Beginning January 1, 2026, a buyer developing exempt-well water use must file a Notice of Intent with DNRC before using the water; the filing fee is $400⁹. DNRC reviews a correct and complete submission within 10 business days, and an authorization gives the applicant 5 years to complete the project, put water to use and file a Notice of Completion⁹. Ask the DNRC Water Resources Regional Office for help and check the Water Rights Query System for parcel-specific Notices of Intent before buying¹⁵.