Bolthole Index

Custer County, Montana

Building permits, zoning and land rules in Custer County, Montana

49Index Score / 100
#43 of 56 in Montana

Unincorporated Custer County, Montana requires a county zoning conformance permit before construction or expansion of a structure, with a narrow exception for a qualifying accessory structure under 100 square feet1. Many small residential buildings are separately exempt from Montana's state building permit, but that exemption does not replace county zoning approval23. Septic work goes through Custer County Environmental Health, with state coordination where applicable4.

At a glance

Building permit
County zoning conformance permit required before construction or expansion in county zoning districts1
Small accessory structure
No county zoning conformance permit below 100 square feet if the structure meets the accessory definition and district standards1
Zoning
County zoning covers unincorporated Custer County; Miles City and Ismay are excluded5
Septic
County Environmental Health handles onsite wastewater, and Montana requires a local drainfield permit46
RV or tiny-home living
Not confirmed; ask the Zoning Administrator about the parcel, district and proposed occupancy5
Owner-builder exemption
No general county exemption was confirmed7
County-road driveway
The Road Department publishes an encroachment permit for a new or changed driveway approach8
Floodplain development
Check for a local floodplain permit before development in a designated hazard area910

Who to call

Planning & zoning

Custer County Zoning Administrator

County zoning conformance, zoning map and land-use questions for unincorporated Custer County

1010 Main Street, Ste. 2, Miles City, Montana, 59301

Health department

Custer County Environmental Health

Onsite wastewater, Sanitarian services and Montana DEQ liaison work in Custer County

Floodplain permits

Custer County Floodplain Development

Floodplain development applications and local floodplain documents

Roads & driveways

Custer County Road Department

County roads, bridges and encroachment permits for driveway or private-road approaches

(406) 232-1970

5125 Valley Drive East Miles City, Montana 59301

Contact details are copied from each office’s official page and were checked against it on September 27, 2026.

Do you need a building permit in Custer County, Montana?

Yes, in the land-use sense: before constructing or expanding a structure in an unincorporated Custer County zoning district, the owner must obtain a zoning conformance permit from the Zoning Administrator1. A qualifying accessory structure under 100 square feet is the stated exception, provided it meets both the accessory-structure definition and the applicable district development standards1. Montana's separate state building-permit program exempts farm and ranch buildings, private garages and storage buildings used by the owner outside a business, and residential buildings with fewer than five dwelling units unless they serve transient guests2. The practical result is that a house may be exempt from a state structural building permit while still needing the county's zoning conformance approval23.

Who issues Custer County building and land-use permits?

The Custer County Zoning Administrator is the first stop for construction on unincorporated land because county rules require that office's zoning conformance permit before construction or expansion1. The county's official zoning map is the final authority on a property's current zoning status and is kept by the Zoning Administrator and County Clerk and Recorder11. Reach the Zoning Administrator at 1010 Main Street, Ste. 2, Miles City, Montana, 5930112. If a nonexempt project falls under Montana's state building-code jurisdiction rather than a certified local program, the state process requires construction plans and a Building Permit/Plan Review Application, followed by approval and payment before permit issuance13. State-required projects may also need separate electrical, plumbing and mechanical permits13.

Does Custer County, Montana have zoning?

Yes. County zoning applies across unincorporated Custer County, while Miles City and the Town of Ismay are excluded from the county zoning district system5. Uses and structures must comply with the parcel's district regulations, and a conditional use may need separate approval and mitigation measures53. The published districts include agricultural, residential, industrial, commercial, public-land and planned-unit-development classifications, and the official zoning map controls the current designation11. The reviewed rules do not establish a single countywide answer for setbacks, minimum dwelling floor area, accessory dwellings or tiny homes, so take the parcel location and a description of the intended use to the Zoning Administrator. The county is considering an updated zoning code, but its official notice says the zoning districts and their extent are not being added or removed by that update12.

How do septic permits work in Custer County?

Custer County Environmental Health handles onsite wastewater administration and provides Sanitarian and Montana DEQ liaison services414. Montana requires a drainfield permit from the local health department even when a property already has a Certificate of Subdivision Approval6. For covered land divisions, Montana DEQ separately reviews sanitation facilities such as water supply, sewage disposal, solid waste and storm drainage, but that review does not replace the local drainfield permit15. Site conditions deserve early attention because only 11.6% of Custer County soils are rated without severe limitations for a conventional septic drain field16. Ask Environmental Health which application, site evaluation, design and installer documentation apply before choosing a house location; the reviewed county material does not confirm the inspection sequence or a general off-grid sanitation exception14.

Can you live in an RV or tiny home in Custer County?

We could not confirm a complete county rule for long-term residential RV occupancy or tiny-home occupancy on private land in unincorporated Custer County. County zoning still applies to uses and structures outside Miles City and Ismay, so the Zoning Administrator should review the parcel's district and the exact proposal before an RV or tiny home is placed or occupied5. A tiny home that involves construction or expansion of a structure may require a zoning conformance permit just like other structures1. Do not use Montana's limits for camping at Fish, Wildlife & Parks public-use sites as an answer for private property; those rules apply to designated public-use sites, not private Custer County land17. Environmental Health should separately confirm the approved wastewater arrangement for any proposed residence4.

Building a home in Custer County: the steps in order

  1. Ask the Zoning Administrator to confirm the parcel's zoning and whether the proposed home is allowed outright or needs conditional-use approval113.
  1. Apply for the county zoning conformance permit before construction begins1.
  1. Ask Custer County Environmental Health for the onsite-wastewater application and obtain the locally required drainfield permit before installation46.
  1. Check the flood map and obtain applicable floodplain approval before developing in a designated hazard area; a conformance permit cannot issue for covered nonresidential work there until the floodplain permits are in hand189.
  1. For access from a county road, ask the Road Department about its encroachment permit; for a new or modified state-highway approach, apply through the appropriate Montana Department of Transportation district office819.
  1. Confirm whether any state electrical, plumbing, mechanical or nonexempt building permits apply before work starts13.

What should you check before buying land in Custer County?

Start with the official zoning map and intended use, because unincorporated Custer County is zoned and conditional-use approval may apply511. Investigate wastewater before fixing the building site: only 11.6% of county soils are rated without severe limits for a conventional drain field16. Confirm well requirements and water availability directly with Environmental Health because the reviewed material does not establish a countywide private-well permit answer4. Check flood status and legal road access, and remember that a new or changed state-highway approach needs state approval919. Custer County averages 14.5 inches of precipitation annually, and severe drought occurred in 11.4% of years, so water supply deserves its own due diligence2021. The effective property-tax rate is about 1.1%, with a median annual bill of about $2,2422223.

Watch-outs

  • A Montana state permit exemption does not erase Custer County's zoning conformance permit requirement for construction in county zoning districts21.
  • Custer County is considering updated zoning regulations in 2026; ask the Zoning Administrator whether the adopted rules changed after the public hearings12.
  • Only 11.6% of Custer County soils are rated without severe limitations for a conventional drain field, so resolve septic feasibility before committing to a building site16.

Sources

  1. Custer County Zoning Regulations, Resolution #2016-31, quoted and re-checked
  2. Building Permits (Montana statewide rule), quoted and re-checked
  3. Custer County Zoning Regulations, Resolution #2016-31, quoted and re-checked
  4. Environmental Health, quoted and re-checked
  5. Custer County Zoning Regulations, Resolution #2016-31, quoted and re-checked
  6. Engineering Infrastructure & Subdivisions (Montana statewide rule), quoted and re-checked
  7. (2026 county census)
  8. Custer County Road Department (custercountymt.gov)
  9. Stream Permitting (Montana statewide rule), quoted and re-checked
  10. Custer County Floodplain Development (custercountymt.gov)
  11. Custer County Zoning Regulations, Resolution #2016-31, quoted and re-checked
  12. Custer County Zoning Administrator (custercountymt.gov)
  13. Building Permits (Montana statewide rule), quoted and re-checked
  14. Custer County Environmental Health (custercountymt.gov)
  15. Engineering Infrastructure & Subdivisions (Montana statewide rule), quoted and re-checked
  16. Share of soils without severe limits for a conventional septic drain field (USDA SSURGO): Bolthole Index county data
  17. Public Use Rules and Regulations (Montana statewide rule), quoted and re-checked
  18. Custer County Zoning Regulations, Resolution #2016-31, quoted and re-checked
  19. Approach Manual for Landowners and Developers (Montana statewide rule), quoted and re-checked
  20. Annual precipitation: Bolthole Index county data
  21. Share of years in severe drought: Bolthole Index county data
  22. Effective property tax rate: Bolthole Index county data
  23. Median property tax bill: Bolthole Index county data

Written September 27, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.

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County locator

Custer County in Montana

49
County map
Custer County highlighted among the Montana counties · colored by Index score

How Custer County scores

Seclusion90100% ev.
Self-Sufficiency18100% ev.
Admin Boringness5590% ev.
Durability42100% ev.
Property Autonomy83100% ev.
Carry Cost8496% ev.

Evidence strength: 98%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$254kTypical home
1.1%Property tax
$1,017Land / acre
14.5"Annual rain
11.4% of yrsSevere drought
16.8 / yr (+12.3)Mid-century 100°F days
21.7 daysMid-century dry spell
1.07" (+5.2%)Mid-century 1-day rain
1.26×Wildfire change factor
100%Forward climate coverage
$2,086Home insurance / yr
-1.1% / yrInsurance growth
0.42%Nonrenewal rate
single ZIP shrunk to state medianInsurance basis
2,881People within 2 hr
216Radius comparison (15 mi)
3.2People / sq mi
16.7%Federal land
61.7%Land at 15% slope or less
11.6%Septic soil without severe limits
265,176 acWorkable land screen
3.6%Wooded land
10.1 tonsBiomass / forest ac
45.3°FAvg temp

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Answers from the rulebook for Custer County

What the ordinances and state agencies actually say — one answer per question, each quoted from the official source and independently re-checked.

Custer County rules

  • Building permitLimited

    Construction or expansion of structures in county zoning districts in unincorporated Custer County.

    • A zoning conformance permit is required before construction or expansion.
    • No county zoning conformance permit is required for an accessory structure under 100 square feet if it meets the accessory-structure definition and district development standards.
    • Montana state law separately exempts residential buildings containing fewer than five dwelling units from state building permits, except when serving transient guests.
    • Municipal requirements may differ in Miles City and Ismay.

    accessory structure threshold: < 100 square feet (Must meet the accessory-structure definition and applicable district development standards.)

    “Prior to construction or expansion of a structure in any zoning district, a landowner shall obtain a zoning conformance permit from the Zoning Administrator to assure compliance with the zoning regulations.”
  • County-wide zoningPresent (with conditions)

    County zoning in unincorporated Custer County, excluding Miles City and Ismay.

    • Miles City and the Town of Ismay are excluded from the county zoning district system.
    • Structures and land uses must conform to the applicable district regulations and may require conditional-use approval.
    “For the purpose as described in Section 1, the entirety of Custer County exclusive of the municipalities of Miles City and the Town of Ismay is hereby divided into the following use classification districts:”
  • Zoning districtsPublished (with conditions)

    Published county zoning districts and map for unincorporated Custer County.

    • The official zoning map is maintained by the Zoning Administrator and County Clerk and Recorder and is available online.
    • Districts listed include AG-1, R-1, R-2, R-3, I-1, C-1, P-1, and PUD.
    • Miles City and Ismay are excluded from the county zoning district system.
    “The official zoning map shall be the final authority as to the current zoning status of properties, buildings and other structures in the county’s jurisdiction and shall be on file with the County Clerk and Recorder’s Office.”
  • Who permits septicCounty (with conditions)

    Onsite wastewater administration in Custer County.

    • The county department also provides DEQ Liaison services and county/state coordination may apply.
    • County materials link to Montana DEQ Circular 4 and subdivision onsite-wastewater standards.
    “The Environmental Health department in Custer County encompasses Sanitarian, DEQ Liaison services at this time.”
  • Subdividing landRegulated (with conditions)

    Subdivision of land within Custer County's jurisdictional area.

    • Within one mile of a third-class city or town, two miles of a second-class city, or three miles of a first-class city, the preliminary plat must be submitted to the city or town for review and comment.
    • If a proposed subdivision lies partly within an incorporated city or town, both governing bodies must approve it.
    • More restrictive applicable regulations control.
    “These regulations govern the subdivision of land within the jurisdictional area of the governing body of Custer County.”
  • Building in a floodplainLimited

    Non-residential uses or structures in designated floodplain areas outside Miles City and Ismay.

    • A conformance permit shall not be issued until all applicable floodplain permits have been issued.
    • The county floodplain regulations are administered and enforced by the Zoning Administrator.
    • The source contains an inserted placeholder rather than an adoption date for the county floodplain regulations.
    “A conformance permit shall not be issued for any non-residential use or structure within a designated floodplain area until all applicable floodplain permits have been issued.”
  • Permit processPublished (with conditions)

    County zoning conformance and conditional-use permitting in unincorporated Custer County.

    • A zoning conformance permit is required before construction or expansion of a structure, subject to the under-100-square-foot accessory-structure exception.
    • Conditional uses require permits and may be approved subject to mitigation measures.
    • Property owners are responsible for obtaining all required state and local permits.
    “Prior to construction or expansion of a structure in any zoning district, a landowner shall obtain a zoning conformance permit from the Zoning Administrator to assure compliance with the zoning regulations.”

Montana rules that apply here

  • Building code adoptedAdopted (with conditions)

    Montana's uniform state building code for residential and commercial buildings statewide.

    • The currently listed codes are amended and adopted through Administrative Rules of Montana Title 24, Chapter 301.
    • Cities, counties, and towns may enforce local building codes, all or in part, only through certified local building-code-enforcement programs.
    • State-owned agencies must be permitted through the Montana Department of Labor and Industry.
    • The listed 2021 International Building, Residential, and Existing Building Codes and related codes are effective June 11, 2022; the listed ASME boiler and pressure-vessel codes are effective November 6, 2021.

    International Building Code edition: 2021 · International Residential Code edition: 2021 · effective date for listed principal codes: 2022-06-11 (ASME boiler and pressure-vessel codes listed on the official page are effective 2021-11-06)

    “In addition, the program is responsible for adopting a uniform state building code, which is enforced statewide for residential and commercial buildings across Montana.”
  • InspectionsLimited

    Buildings and other projects requiring permits under Montana state building-code jurisdiction; certified local governments may perform inspections within their certified jurisdictional areas.

    • The Montana Building Codes Program performs inspections for projects requiring a permit under state jurisdiction.
    • The permit holder must notify the inspector when work is ready for inspection and provide access for required inspections.
    • Cities, counties, and towns may enforce local building codes and perform inspections only through certified local government programs; remaining areas fall under the state Building Codes Program.
    “The BC Program establishes and enforces statewide codes by issuing permits and performing inspections.”
  • Certificate of occupancyLimited

    Buildings constructed in accordance with the Montana state building code or a county, city, or town building code.

    • The certificate must certify that the building conforms to the applicable building regulations.
    • The statute addresses certificates for buildings constructed under the state or local building code; it does not establish a universal certificate requirement for every structure or every occupancy.
    “A certificate of occupancy for a building constructed in accordance with the provisions of the state building code or county, city, or town building code must certify that the building conforms to the requirements of the building regulations applicable to it.”
  • Septic permitRequired

    Installation of a drainfield in Montana, including property already covered by a Certificate of Subdivision Approval.

    • A Certificate of Subdivision Approval does not replace the drainfield permit.
    • The cited page identifies the local health department as the permitting authority.
    “Yes, even thought you have a COSA, a drainfield permit is still required by the local health department.”
  • Driveway accessLimited

    New or modified driveway approaches intersecting Montana state highways, and changes in use of property abutting a state highway or an existing approach.

    • A new or modified approach requires either an approach permit or a right-of-way agreement.
    • A change in property use or change in use of an existing approach requires a new approach permit.
    • The landowner is responsible for obtaining the new permit.
    • The application must be made to the appropriate MDT District Office.
    • A detailed site plan and Environmental Checklist Form are required.
    • The requirement concerns state highways; local roads may be administered by local governments.
    “ALL NEW OR MODIFIED APPROACHES REQUIRE EITHER AN APPROACH PERMIT OR A RIGHT-OF-WAY AGREEMENT.”
  • Short-term rentalsLimited

    Short-term rentals operated in Montana.

    • A Property Manager license is required unless the operator qualifies for an exemption under MCA § 37-56-104 or MCA § 50-51.
    • Local land-use, lodging, tax, and public-accommodation requirements may also apply.

    application fee: 50 USD

    “Short Term Rentals: A Property Manager license is required for short term rentals unless an operator qualifies for an exemption”
  • Permit feesVariable (with conditions)

    State building permit and plan-review fees for state-administered building permits.

    • The building permit fee is calculated by the bureau under IBC Section 109.2 as modified by ARM 24.301.138.
    • A plan review fee is charged in addition to the building permit fee and equals 35 percent of the building permit fee.
    • Both fees must be paid before the building permit is issued.
    • Local governments certified to enforce the state building code may establish their own permit fees and valuation method.

    plan review fee: 35 percent of building permit fee

    “The plan review fee is 35 percent of the building permit fee as established in Table 109.2.”
  • Campground & park staysLimited

    Camping in Montana Fish, Wildlife & Parks public-use sites.

    • Camping is prohibited except in areas specifically designated or marked for camping.
    • A camping unit, vehicle, equipment, or personal items may not be left overnight without a person present.
    • Camping longer than 7 nights at one or more campsites in a public use area during any consecutive 30-day period is prohibited unless otherwise posted by the department.
    • Designated occupancy limits must not be exceeded.
    • Special-use-permit terms must be followed unless otherwise posted.
    • Campsites must be vacated by 1 p.m. on the day of departure; camping facilities must be vacated by 12 p.m. on the day of departure.

    maximum camping duration: <= 7 nights per consecutive 30-day period (unless otherwise posted by the department) · campsite departure time: 1 p.m. · camping-facility departure time: 12 p.m.

    “Unless otherwise posted by the department, within a public use site it is prohibited to: [...] camp at one or more campsites in a public use area for a period of longer than 7 nights during any consecutive 30-day period, beginning with the first night occupied unless otherwise posted by the department;”
  • county zoning authorityGeneral

    Montana boards of county commissioners adopting zoning regulations for all or parts of their jurisdictional areas, including unincorporated land.

    • The board of county commissioners must have adopted a growth policy pursuant to Montana Code Annotated chapter 1.
    • Zoning regulations must be adopted in accordance with Title 76, chapter 2.
    • The statute also contains a temporary provision for counties that adopted a master plan before October 1, 1999; that provision authorized adoption or revision only until October 1, 2006.
    “a board of county commissioners that has adopted a growth policy pursuant to chapter 1 is authorized to adopt zoning regulations”

Still unanswered

We looked and could not find an official answer yet. Silence is not permission — ask the county directly.

  • Owner-builder exemption — Owner-builder exemptions from building or zoning approvals.
  • Minimum dwelling size — Minimum dwelling size in unincorporated Custer County.
  • Living in an RV — Long-term or residential occupancy of recreational vehicles on private land.
  • Tiny homes — Tiny-home occupancy in unincorporated Custer County.
  • Accessory dwellings — Accessory dwelling units in unincorporated Custer County.
5 more unanswered
  • Septic inspection
  • Off-grid sanitation
  • Well permit
  • Mandatory utility hookup
  • Agricultural exemption

Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.

Living off-grid in Custer County, Montana

Is Custer County a good place to live off-grid or homestead?

Custer County scores 49/100 on the Bolthole Index, a solid county profile. Its strengths: deep seclusion — about 216 people within 15 miles and manageable long-term carry cost. Watch-outs: weak self-sufficiency basics: only 14.5″ of rain a year.

Do you need a building permit in Custer County, Montana?

Custer County requires a building permit only in limited cases (such as floodplains or specific zones), and it enforces county zoning. Onsite septic is permitted by Custer County Environmental Health / Sanitarian (with Montana DEQ liaison). These answers are quoted from official sources and independently re-checked. Rules change and cities within the county differ — always confirm with the county before you buy or build.

How much does land cost in Custer County, Montana?

Land in Custer County runs about $1,017 per acre, based on the latest county data.

What is the water situation in Custer County?

Custer County gets about 14.5" of rain a year, with severe drought in roughly 11.4% of years.

How remote is Custer County?

A typical private-land location has about 216 people within 15 miles and 44,850 within 100 miles. These radius catchments are the published fallback where road routing is unavailable.

Off-grid gear

Going off-grid in Custer County means bringing your own water and power. The kit we’d start with:

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How Custer compares in Montana

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