Petroleum County, MT: No Building Permit, No Zoning

Unincorporated Petroleum County, Montana has no county building permit and no county-adopted building code, and a typical private home also falls under the state's exemption for residential buildings with fewer than five dwelling units.¹²³ The county has no zoning, so no county rule sets setbacks, minimum home size, or RV and tiny-home occupancy on a rural parcel.⁴ Septic is separate: Montana DEQ handles sanitation approval, and a drainfield permit still comes from a local health department.⁵⁶

At a glance

Building permit: Not required by the county; the state also exempts most single-family homes from its own permit⁷³
Zoning: No countywide zoning in unincorporated areas; subdivision review, sanitation approval and floodplain permits still apply⁸⁹
Septic: Sanitation approval (COSA) comes from Montana DEQ; a drainfield permit still comes from a local health department¹⁰⁶
Owner-builder exemption: Available for your own property; the contractor-licensing exemption has limits for property improved for prompt resale¹¹¹²
Wells: No permit needed for a well pumping 35 gallons per minute or less and up to 10 acre-feet a year, but a Notice of Intent form is required starting January 1, 2026¹³
Subdivision: Regulated: new lots are reviewed against the county Growth Policy and county subdivision regulations¹⁴
RV, tiny home, minimum home size: No county rule in unincorporated areas because the county has no zoning; the Town of Winnett and state sanitation rules are separate⁴

Who to call

Roads & driveways

Petroleum County Road Department

County road maintenance and access questions for Petroleum County

406-429-5251

302 E Main, PO Box 226, Winnett, MT 59087-0226

Also useful

Petroleum County Board of Commissioners

County Growth Policy administration and subdivision plat approval for Petroleum County

406-429-2121

302 East Main, Winnett, MT 59087

Building permits

Montana Building Codes Program

State building permits and plan review for construction in Petroleum County that does not qualify for a state exemption

406-841-2056

buildingcodes@mt.gov

P.O. Box 200517, Helena, MT 59602

Septic permits

Montana Department of Environmental Quality, Engineering, Infrastructure & Subdivisions

Subdivision sanitation review and Certificates of Subdivision Approval (COSA) for Petroleum County

406-444-2544

2401 Colonial Dr., Helena, MT 59601

Contact details are copied from each office’s official page and were checked against it on October 9, 2026.

Off-grid gear

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

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

Petroleum County does not impose a building permit beyond Montana's requirements, and the county has not adopted its own building code¹². Montana exempts farm and ranch buildings and residential buildings with fewer than five dwelling units unless they serve transient guests³. A typical private single-family home therefore needs no county or state building permit³. Montana's uniform code still governs projects within state jurisdiction, including nonexempt projects in Petroleum County¹⁵. For a state-permitted project, obtain the building permit before construction and before related plumbing, mechanical or electrical work begins¹⁶.

Who issues building permits in Petroleum County, and how do you reach them?

Petroleum County has no county-adopted building code and no full-time building official, so there is no county office that issues building permits.² If a project is not exempt, the state issues the building permit: contact the Montana Building Codes Program at 406-841-2056 or buildingcodes@mt.gov.¹⁷ State applicants submit plans and the Building Permit/Plan Review Application; plan review averages three weeks, and written responses to review comments and payment are required before issuance.¹⁶ State fees depend on project valuation, with an additional plan-review fee equal to 35 percent of the building-permit fee.¹⁸

What stays with the county: the Road Department for county-road access, and the Board of Commissioners for subdivision and Growth Policy questions.¹⁹²⁰ The county's Planning Department also runs floodplain permits, which cost $250 per permit under the 2026 fee schedule.²¹ Septic and drainfield permits are separate again, with Montana DEQ and the local health department.⁶

Does Petroleum County, Montana have zoning?

Petroleum County has no countywide zoning, including in unincorporated areas.⁸ Because there is no zoning ordinance, no county rule sets minimum dwelling size, setbacks, lot coverage or building height on an unincorporated parcel.⁴ Zoning being absent does not remove subdivision review, sanitation approval, floodplain controls or other non-zoning requirements.⁸ New lots remain subject to the county's subdivision regulations and review against its Growth Policy.¹⁴

For a subdivision, Montana's sanitation rules require each proposed lot to be large enough for the septic system, a drainfield replacement area, the water supply and all permanent structures, and the reviewing authority may require larger lots to protect health or water quality.²² Rules inside the Town of Winnett are separate from the countywide answer; we could not confirm them, so ask the town before buying a lot within its limits.

How do septic permits work in Petroleum County?

Montana DEQ handles subdivision sanitation approval in Petroleum County¹⁰²³. For property subject to that review, DEQ issues the Certificate of Subdivision Approval covering the approved use, water source, wastewater method and stormwater mitigation⁵. A COSA must be issued before facilities requiring sewer or water are developed, but that rule does not require every parcel to connect to municipal utilities²⁴. A separate drainfield permit remains required from the applicable local health department, which we could not identify; ask DEQ or the county commissioners who currently serves Petroleum County⁶. About 21.6% of county soils lack severe limitations for a conventional drainfield, so obtain a site evaluation rather than assuming a standard system will work²⁵.

Can you live in an RV or tiny home on your land in Petroleum County?

Unincorporated Petroleum County has no county rule on long-term RV living, tiny homes, manufactured homes or accessory dwellings, because the county has no zoning ordinance.⁴ That removes the county as a barrier, not the other requirements: any dwelling that generates wastewater still needs Montana DEQ sanitation approval and a drainfield permit from the local health department.⁵⁶ Montana's camping limits for state public-use sites apply to state recreation land, not private property, so they do not answer residential RV use here.²⁶

Private covenants, a lender or an insurer may still set limits, and the Town of Winnett's rules for a lot inside the town are unconfirmed. Before buying for one of these uses, ask the Board of Commissioners to confirm nothing parcel-specific applies.²⁰

How do you build a home in Petroleum County, Montana, step by step?

Confirm whether the state exemption applies; residential buildings with fewer than five dwelling units are exempt unless they serve transient guests³.
If a state permit is required, submit plans and the Building Permit/Plan Review Application before construction or related trade work begins¹⁶¹⁷.
Resolve DEQ sanitation approval before developing facilities that require water or sewer, then obtain the separate drainfield permit from the applicable local health department²⁴⁶.
For a qualifying well pumping no more than 35 gallons per minute and 10 acre-feet yearly, file the required groundwater notice before use¹³.
If the parcel touches a stream, ask the county floodplain administrator whether it lies in a designated Special Flood Hazard Area and, if so, get a floodplain permit before building.⁹
If creating a lot, start subdivision review with the Board of Commissioners¹⁴²⁰.
On state-permitted work, call the inspector at least 24 hours before the requested inspection; the inspector has 72 hours to perform it²⁷.

What should you check before buying land in Petroleum County, Montana?

Petroleum County has about 554 residents, so verify contractor availability and travel to services before buying.²⁸ About 37.4% of county land is federally owned, making parcel boundaries and legal access worth checking carefully.²⁹ Only 21.6% of county soils lack severe limitations for a conventional drainfield, so make sanitation feasibility part of due diligence.²⁵

For water, a well using 35 gallons per minute or less and no more than 10 acre-feet per year may qualify for the exempt-well exception, which since January 1, 2026 requires a Notice of Intent filed with DNRC and a $400 form fee.³⁰ A new or modified driveway onto a state highway needs an approach permit or right-of-way agreement from the Montana Department of Transportation; the county-road driveway process could not be confirmed.³¹ Development in a designated Special Flood Hazard Area needs a floodplain permit, and the floodplain administrator decides whether the stream has one.⁹

The median property-tax bill is about $1,261 yearly, with an effective rate near 0.7%.³²³³ Severe drought occurs in roughly 12.1% of years, a practical concern for a private water plan.³⁴ The nearest city of 100,000 or more is about 96 miles from the county center.³⁵

Watch-outs

Petroleum County has no county building permit, but nonexempt projects remain under Montana's uniform building code and state permit process.¹¹⁵
A drainfield permit is still required from a local health department even after Montana DEQ issues a Certificate of Subdivision Approval, and no source identifies which health department currently serves Petroleum County; confirm this before you plan a septic system⁶.
The county has no zoning, but floodplain permits still apply in a designated Special Flood Hazard Area, at $250 per permit.²¹⁹
We could not confirm the Town of Winnett's own zoning or building rules, which are separate from the countywide answer.⁸

Sources

Written October 9, 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.

Compared with neighboring counties

Like all 6 of its neighbors, Petroleum County requires no county building permit for a home.

Rule	Petroleum County	Fergus County	Musselshell County	Garfield County	Golden Valley County	Phillips County	Yellowstone County
Building permit	Not required	Not required	Not required	Not required	Not required	Not required	Not required
County zoning	No	No	No	Not published	Not published	Not published	Yes
Septic permits	MT Dept. of Env. Quality	County Health Dept.	County Sanitation Services	Not published	County Sanitarian	County Health Dept.	RiverStone Health

How Petroleum County scores

Seclusion89100% ev.

Self-Sufficiency11100% ev.

Admin Boringness88100% ev.

Durability35100% ev.

Property Autonomy83100% ev.

Carry Cost8494% ev.

Evidence strength: 100%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$212kTypical home

0.7%Property tax

$1,059Land / acre

14.3"Annual rain

12.1% of yrsSevere drought

14.2 / yr (+11.1)Mid-century 100°F days

22.3 daysMid-century dry spell

0.94" (+6.4%)Mid-century 1-day rain

1.24×Wildfire change factor

100%Forward climate coverage

state median fallbackInsurance basis

334Radius comparison (15 mi)

0.3People / sq mi

37.4%Federal land

75.6%Land at 15% slope or less

21.6%Soils rated "not limited" for septic (strict USDA rating)

223,985 acWorkable land screen

4.9%Wooded land

7 tonsBiomass / forest ac

46.2°FAvg temp

Answers from the rulebook for Petroleum County

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

Petroleum County rules

Building permitNot required
County-imposed building permit requirements for buildings erected in Petroleum County.
- Petroleum County does not impose county building permit requirements beyond requirements imposed by the State of Montana.
- State building permit requirements and any applicable local jurisdiction requirements may still apply.
“Petroleum County does not impose any building permit requirements other than those required by the State of Montana for the buildings erected in the County.”
Petroleum County Growth Policy 2022 Revision ↗Re-checked Sep 11, 2026
Owner-builder exemption · follows from the permit answerNot needed
Unincorporated Petroleum County: no county building permit is required, so there is no permit to be exempt from and you may build your own home. State licensing for electrical, plumbing and HVAC work may still apply.
- Petroleum County does not impose county building permit requirements beyond requirements imposed by the State of Montana.
- State building permit requirements and any applicable local jurisdiction requirements may still apply.
“Petroleum County does not impose any building permit requirements other than those required by the State of Montana for the buildings erected in the County.”
Petroleum County Growth Policy 2022 Revision ↗Re-checked Sep 11, 2026
Building code adoptedNot adopted
Building-code adoption by Petroleum County.
- The official hazard mitigation plan states that the county does not have existing building codes and does not plan to adopt any.
- State building-permit exemptions and state code requirements may still apply to particular projects.
- The same plan reports no full-time building official for Petroleum County.
“The county does not have any existing building codes”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
County-wide zoningAbsent
Countywide zoning in Petroleum County, including unincorporated areas.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Zoning districts · by state lawNot published
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Minimum dwelling size · by state lawNone
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Setbacks · by state lawNone
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Lot coverage · by state lawNone
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Building height · by state lawNone
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Living in an RV · by state lawUnrestricted
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Camping on your land · by state lawUnrestricted
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Tiny homes · by state lawUnrestricted
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Manufactured homes · by state lawUnrestricted
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Accessory dwellings · by state lawUnrestricted
Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance.
- Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits.
- The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance.
- Floodplain, subdivision, sanitation, and other non-zoning requirements may still apply.
“A Growth Policy is not a regulation or ordinance, but it serves as the legal basis for enacting them.”
Central Montana Central Region Hazard Mitigation Plan, Annex K: Petroleum County ↗Re-checked Oct 1, 2026
Subdividing landRegulated (with conditions)
Creation of new lots and other subdivisions in Petroleum County, subject to the Montana Subdivision and Platting Act, Petroleum County's subdivision regulations, and applicable exemptions.
- Petroleum County subdivisions are reviewed for compliance with the Petroleum County Growth Policy and county subdivision regulations.
- The county growth policy states that the county completed an update of its subdivision regulations compliant through the 2015 legislative-session changes.
- The county's subdivision regulations and evaluation process are stated to be available at the Petroleum County courthouse.
- State-law exemptions may apply to particular divisions of land.
“Because of the possibility for adverse effects on resources, subdivisions will be reviewed for compliance to the Petroleum County Growth Policy as well as compliance with subdivision regulations recently adopted by the County.”
Petroleum County Growth Policy 2022 Revision ↗Re-checked Sep 11, 2026
Building in a floodplainRequired
Development in a designated Special Flood Hazard Area in Petroleum County.
- The local floodplain administrator determines whether an SFHA is designated for the stream of interest.
- Covered development includes fill, roads, bridges, culverts, transmission lines, irrigation facilities, storage of equipment or materials, excavation, manufactured homes, and new construction, additions, or substantial improvements to residential and commercial buildings.
- Applications are obtained from the local floodplain administrator.
- Local fees and timelines apply.
Floodplain Permit: 250 USD (Fee schedule applies as of January 1, 2026.)
“Anyone planning new development within a designated Special Flood Hazard Areas (SFHA). [...] Any development including, but not limited to, placement of fill, roads, bridges, culverts, transmission lines, irrigation facilities, storage of equipment or materials, and excavation; new construction/development, placement, or replacement of manufactured homes; and new construction, additions, or substantial improvements to residential and commercial buildings.”
Stream Permitting ↗Re-checked Oct 5, 2026
One more reviewed finding on this topic
- Required — New development within a designated Special Flood Hazard Area in Petroleum County, including placement of fill, roads, bridges, culverts, transmission lines, irrigation facilities, storage of equipment or materials, excavation, manufactured homes, and new construction, additions, or substantial improvements to residential and commercial buildings.
  “Anyone planning new development within a designated Special Flood Hazard Areas (SFHA).”
  Stream Permitting ↗Re-checked Oct 5, 2026
Permit feesPublished
Petroleum County Planning Department floodplain permits, extensions, appeals, variance requests, violation inspections, after-the-fact permits, special floodplain meetings or hearings, and engineering/environmental vendor services.
- The fee schedule applies as of January 1, 2026.
- Engineering and environmental vendor charges are by vendor.
- The listed fees are specifically for floodplain services; no general county building-permit fee schedule was located.
Floodplain Permit: 250 USD · Floodplain Permit Extension: 75 USD · Floodplain Appeal: 250 USD · Floodplain Variance Request: 250 USD · Floodplain Violation inspection: 250 USD · After the Fact Permit: 500 USD · Special Floodplain Meeting/Hearing: 250 USD · Engineering & Environmental Vendors: Charges by Vendor
“NOW, THEREFORE, BE IT RESOLVED that the following Fee Schedule rates shall apply as of January 1, 2026; Planning Department-Floodplain Floodplain Permit $250.00 Floodplain Permit Extension $75.00 Floodplain Appeal $250.00 Floodplain Variance Request $250.00 Floodplain Violation inspection $250.00 After the Fact Permit $500.00 Special Floodplain Meeting/ Hearing $250.00 Engineering & Environmental Vendors Charges by Vendor”
Resolution No. 2026-4: Fee Schedule ↗Re-checked Oct 5, 2026
One more reviewed finding on this topic
- Published (with conditions) — Planning Department floodplain permits, extensions, appeals, variance requests, violation inspections, after-the-fact permits, special floodplain meetings or hearings, and engineering or environmental vendor services in Petroleum County.
  “Floodplain Permit $250.00 Floodplain Permit Extension $75.00 Floodplain Appeal $250.00 Floodplain Variance Request $250.00 Floodplain Violation inspection $250.00 After the Fact Permit $500.00”
  Resolution No. 2026-4: Fees for Permits, Inspections, and Services ↗Re-checked Oct 5, 2026
Permit processPartial
New development in a designated Special Flood Hazard Area in Petroleum County.
- A local floodplain administrator must determine whether an SFHA has been designated for the stream of interest.
- Activities requiring a permit include placement of fill, roads, bridges, culverts, transmission lines, irrigation facilities, storage of equipment or materials, excavation, manufactured-home placement or replacement, and new construction, additions, or substantial improvements to residential and commercial buildings.
- Permit applications are available from the local floodplain administrator.
- Application fees and timelines are established by the local government and vary widely statewide.
- The complete Petroleum County ordinance, exemptions, variance criteria, and detailed application process were not located.
“Anyone planning new development within a designated Special Flood Hazard Areas (SFHA). Check with local floodplain administrator to determine whether a Special Flood Hazard Areas (SFHA) has been designated for the stream of interest. [...] Permit applications are available from the local floodplain administrator. Application fees and timelines are established by the local government and vary widely throughout the state.”
Stream Permitting ↗Re-checked Oct 5, 2026

Montana rules that apply here

InspectionsRequired
Buildings in Petroleum County requiring a Montana state building permit.
- The inspection requirement applies to projects subject to state building-code jurisdiction and requiring a building permit.
- The permit holder must call the building inspector at least 24 hours before a requested inspection.
- The inspector has 72 hours from notification to perform the requested inspection.
- Farm and ranch buildings, mining buildings on mining property, qualifying petroleum refineries and pulp and paper mills, qualifying residential buildings with fewer than five dwelling units, and qualifying private garages and private storage buildings are exempt from the state building permit and therefore are not covered by this permit-based inspection process.
- Certified local jurisdictions may conduct inspections for permit types they are certified to regulate.
advance inspection notice: 24 hours · inspector response period: 72 hours
“It is the responsibility of the permit holder to call the building inspector at least 24 hours before a requested inspection”
Is a State Building Permit Needed? ↗Re-checked Sep 11, 2026
One more reviewed finding on this topic
- Limited — Buildings and other projects requiring permits under Montana state building-code jurisdiction; certified local governments may perform inspections within their certified jurisdictional areas.
  “The BC Program establishes and enforces statewide codes by issuing permits and performing inspections.”
  Building Permits ↗Re-checked Sep 11, 2026
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.”
50-60-107. Certificate of occupancy, MCA ↗Re-checked Sep 11, 2026
Minimum lot sizeSpecified
Minimum lot or parcel size for proposed subdivision lots, condominium areas, and areas proposed for permanent multiple recreational-camping-vehicle or mobile-home spaces under Montana sanitation review, including applicable projects in Petroleum County.
- Each proposed lot must be sufficient to accommodate required sanitation facilities, drainfield replacement area, water supply, and all permanent structures.
- Facilities must comply with ARM 17.36.323 setbacks, subject to the stated exception for existing sewage systems.
- Drainfield mixing zones must comply with ARM 17.36.322(5).
- Well isolation zones must comply with ARM 17.36.330(4).
- Lots created before July 1, 1973, for which sanitary restrictions are proposed to be lifted, remain subject to the specified requirements and ARM 17.36.106(3).
- The reviewing authority may require larger lots when necessary to protect human health or water quality.
- The rule does not state a single statewide acreage minimum; adequacy is determined by the listed site and facility criteria.
lot size standard: sufficient size to satisfy sanitation, setback, water-supply, structure, easement, and utility criteria (The reviewing authority may require larger lots to protect human health or water quality.)
“This rule sets out, for purposes of the review of proposed subdivisions, the requirements for minimum lot or parcel size.”
ARM 17.36 Subchapter 3 — Subdivision Requirements ↗Re-checked Oct 7, 2026
Who permits septicState (with conditions)
Subdivision sanitation approval and Certificates of Subdivision Approval for applicable property in Petroleum County.
- The Montana Department of Environmental Quality issues the Certificate of Subdivision Approval.
- The COSA addresses the property use, potable water source, wastewater disposal method, and stormwater mitigation.
- A COSA requirement applies only where the property is subject to subdivision sanitation review; the DEQ page separately describes sanitary restrictions and no-facilities exemptions.
“sanitation approval from the Montana Department of Environmental Quality.”
Engineering Infrastructure & Subdivisions ↗Re-checked Sep 11, 2026
One more reviewed finding on this topic
- Mixed (with conditions) — Montana statewide sanitation and septic regulation, including subdivision sanitation review and drainfield permitting.
  “The DEQ Subdivision Program reviews divisions of land comprising less than 20 acres [...] This review is limited to sanitation facilities, including the water supply, sewage disposal, solid waste disposal, and storm drainage systems. [...] Yes, even thought you have a COSA, a drainfield permit is still required by the local health department.”
  Engineering Infrastructure & Subdivisions ↗Re-checked Sep 11, 2026
Septic permitRequired
Drainfield installation associated with a COSA in Petroleum County, where the local health department is the permitting authority identified by the Montana DEQ.
- A drainfield permit remains required even after a COSA has been issued.
- The official source does not identify the specific local health department serving Petroleum County.
“required by the local health department.”
deq.mt.gov ↗Re-checked Sep 11, 2026
One more reviewed finding on this topic
- Required — Installation of a drainfield in Montana, including property already covered by a Certificate of Subdivision Approval.
  “Yes, even thought you have a COSA, a drainfield permit is still required by the local health department.”
  Engineering Infrastructure & Subdivisions ↗Re-checked Sep 11, 2026
Well permitLimited
New groundwater developments in Montana using 35 gallons per minute or less and no more than 10 acre-feet per year.
- All water uses starting after June 30, 1973, require a water right either through a water-use permit or an exception to the permitting process.
- The development may qualify for the exception; qualification is not automatic.
- Completed groundwater uses that meet the permit exception receive a Groundwater Certificate rather than a water permit.
- A permitted water right is required for a combined appropriation from the same source by two or more wells or developed springs exceeding 10 acre-feet, regardless of flow rate.
- All lots in a multi-phase subdivision must share a combined water-use limit of 10 acre-feet per year to qualify for a permit exception.
- Beginning January 1, 2026, a water user intending to develop water use through a permit exception must file a Notice of Intent with DNRC before using water from an exempt well.
- DNRC reviews a correct and complete Notice of Intent within 10 business days; if eligible, it authorizes the Notice of Intent and gives the user five years to complete the project, put the water to use, and file a Notice of Completion.
- If the proposed use is not eligible, the Notice of Intent is denied and the user is directed to the water-right permit process.
- The Notice of Intent filing fee is $400.
- An authorized Notice of Intent expires after five years, with an opportunity for one five-year extension.
maximum flow rate: <= 35 gpm · maximum annual volume: <= 10 acre-feet per year · Notice of Intent fee: 400 USD (Beginning January 1, 2026) · Notice of Intent review period: 10 business days (For a correct and complete Notice of Intent) · authorized Notice of Intent term: 5 years (One five-year extension opportunity is available)
“Permit Exceptions, a.k.a. Exempt Wells: Small groundwater developments that use 35 gpm or less and do not exceed 10 acre-feet per year are known as “exempt wells” and may qualify for an exception to the water permit process.”
Exempt Well Updates and Information ↗Re-checked Oct 5, 2026
4 more reviewed findings on this topic
- Limited — Groundwater wells in Petroleum County qualifying for Montana's groundwater permit exception.
  “35 gallons per minute or less, not to exceed 10 acre-feet per year”
  Exceptions To Permit Requirements ↗Re-checked Sep 11, 2026
- Required — Surface-water uses and groundwater uses in Petroleum County exceeding 35 gallons per minute or 10 acre-feet per year.
  “Water Permits: A water permit is required for all surface water use and groundwater uses over 35 gallons per minute (gpm) or 10 acre-feet per year.”
  Exempt Well Updates and Information ↗Re-checked Oct 5, 2026
- Limited — Small groundwater developments in Petroleum County using 35 gallons per minute or less and not exceeding 10 acre-feet per year.
  “Small groundwater developments that use 35 gpm or less and do not exceed 10 acre-feet per year are known as “exempt wells” and may qualify”
  Exempt Well Updates and Information ↗Re-checked Oct 5, 2026
- Required — Surface-water uses and groundwater uses exceeding 35 gallons per minute or 10 acre-feet per year in Montana.
  “Water Permits: A water permit is required for all surface water use and groundwater uses over 35 gallons per minute (gpm) or 10 acre-feet per year.”
  Exempt Well Updates and Information ↗Re-checked Oct 5, 2026
Mandatory utility hookupConditional
Development of sewer or water facilities on lots subject to Montana subdivision sanitation review, including applicable lots in Petroleum County.
- A COSA must be issued before developing facilities that require sewer or water.
- The source does not establish that every parcel must connect to municipal water or sewer.
“prior to developing facilities that require sewer or water.”
Engineering Infrastructure & Subdivisions — Sanitary Restrictions FAQ ↗Re-checked Sep 11, 2026
Agricultural exemptionConditional
Divisions made outside platted subdivisions in Petroleum County by gift, sale, or agreement to buy and sell where the landowner enters into a covenant with the governing body requiring the divided land to be used exclusively for agricultural purposes.
- The method of disposition must not be adopted for the purpose of evading Title 76, chapter 3.
- The division may be of a tract of record of any size, regardless of the resulting lot size, but remains subject to the surveying requirements of 76-3-401 and applicable zoning regulations adopted under Title 76, chapter 2.
- The covenant must run with the land and provide that the divided land will be used exclusively for agricultural purposes, subject to 76-3-211.
- The county treasurer must certify that all real property taxes and special assessments assessed and levied on the land to be divided have been paid; centrally assessed property taxes may be prorated by the Department of Revenue, and the owner must ensure the prorated taxes and special assessments are paid before the division is made.
- The governing body shall examine the division to determine whether Title 76, chapter 3 requirements apply, may establish a reasonable examination fee not exceeding $400, and shall approve or deny a complete application within 20 working days.
- The application must include the applicant's affidavit stating the applicant's intentions, including that the exemption is not being used to evade Title 76, chapter 3; the governing body may not force the applicant to appear during the examination period.
- The governing body may not impose approval conditions except conditions necessary to ensure compliance with the survey requirements of Title 76, chapter 3, part 4.
- A change to a nonagricultural use subjects the division to subdivision review under parts 5 and 6 unless the governing body, in its discretion, revokes the covenant because the original lot lines are restored through aggregation, a government or public entity seeks public use under the governing body's review criteria, or the land is annexed into a municipality.
- For a proposed revocation based on public use, the governing body must hold a public hearing, issue written findings and a decision within 15 days after the hearing, and record an approved revocation with the clerk and recorder.
- Revocation does not affect sanitary restrictions imposed under Title 76, chapter 4.
maximum examination fee: <= 400 USD · examination decision deadline: 20 working days (Begins upon receipt of an application containing all materials and information required for review.) · public-use revocation findings deadline: 15 days after public hearing (Applies when revocation is proposed because a government or public entity seeks public use.)
“the following divisions or aggregations [...] are not subdivisions under this chapter [...] (c) divisions made outside of platted subdivisions [...] used exclusively for agricultural purposes”
76-3-207. Divisions or aggregations of land exempted from review but subject to survey requirements and zoning regulations -- exceptions -- fees for examination of division -- definitions ↗Re-checked Oct 5, 2026
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.”
Approach Manual for Landowners and Developers ↗Re-checked Sep 11, 2026
One more reviewed finding on this topic
- Required — New or modified driveway approaches connecting property in Petroleum County to a Montana state highway.
  “ALL NEW OR MODIFIED APPROACHES REQUIRE EITHER AN APPROACH PERMIT OR A RIGHT-OF-WAY AGREEMENT. CHANGES IN THE USE OF PROPERTY ABUTTING A STATE HIGHWAY OR CHANGE IN USE OF AN EXISTING APPROACH REQUIRE A NEW APPROACH PERMIT.”
  Approach Manual for Landowners and Developers ↗Re-checked Oct 5, 2026
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”
Property Management Program ↗Re-checked Sep 11, 2026
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;”
Public Use Rules and Regulations ↗Re-checked Sep 11, 2026
One more reviewed finding on this topic
- Limited — Dispersed and designated-campground temporary camping on legally accessible Montana state trust land administered by DNRC.
  “Dispersed camping is allowed on state trust land with the appropriate permit and with certain restrictions. Dispersed camping on state trust land is allowed with a Conservation License. Camping that is incidental to hunting or fishing is permitted through your conservation license, and no additional permitting is required. Group camping requires a special recreational use license. On leased or licensed land: 2 days On unleased/unlicensed land: 16 days within a 30-day period Within designated campground: 16 days within a 30-day period”
  Camping ↗Re-checked Oct 1, 2026
county zoning authorityGeneral
Montana county boards of commissioners' authority to adopt zoning regulations, including in unincorporated portions of established jurisdictional areas.
- The board of county commissioners must have adopted a growth policy pursuant to Title 76, chapter 1.
- Zoning may be adopted for all or parts of the jurisdictional area in accordance with Title 76, chapter 2, part 2.
- Within unincorporated portions of an established jurisdictional area, the board may establish zoning regulations by resolution or divide the county into zoning districts.
- Zoning regulations may regulate the erection, construction, reconstruction, alteration, repair, location, or use of buildings or structures and the use of land.
- An action challenging creation of a zoning district or adoption of zoning regulations must be commenced within 6 months after the board's order.
- Regulations in one district may differ from those in other districts.
- The statute also states that zoning regulations may not treat manufactured housing or factory-built housing units differently from other residential units, subject to the statutory presumption concerning placement.
challenge period: 6 months (after the date of the board order creating the district or adopting the regulations)
“For the purpose of promoting the public health, safety, morals, and general welfare, a board of county commissioners that has adopted a growth policy pursuant to chapter 1 is authorized to adopt zoning regulations for all or parts of the jurisdictional area in accordance with the provisions of this part.”
76-2-201. County zoning authorized, MCA ↗Re-checked Oct 1, 2026
One more reviewed finding on this topic
- General — Montana county boards of commissioners adopting zoning regulations for all or parts of their jurisdictional areas, including unincorporated portions where the statutory prerequisites are met.
  “a board of county commissioners that has adopted a growth policy pursuant to chapter 1 is authorized to adopt zoning regulations”
  Montana’s 2019 Land Use & Planning Statutes ↗Re-checked Oct 1, 2026
county building authorityGeneral
Montana counties may adopt and enforce building codes and require construction permits for residential construction in unincorporated county areas, subject to the statutory certification, geographic, code-content, and permit requirements.
- A county may adopt a building code by ordinance or resolution, or authorize adoption by administrative action.
- A county may adopt its building code on a countywide basis unless a city or town within the county has adopted a building code; the county may not enforce its county building code within that city or town.
- The county code-enforcement program must be certified by the Montana Department of Labor and Industry.
- The current adopted code, current fee list, and current enforcement plan must be filed with and approved by the Department.
- Inspectors must satisfy the stated state-licensing or approved national-certification requirements.
- Except for voluntary incentive-based energy-conservation standards, the county may not adopt or enforce a building code more stringent than the code adopted by the Department or required by state law.
- The county may prohibit construction from commencing until the required permit is issued after compliance is shown.
- The general construction-permit requirement applies to buildings subject to Title 50, chapter 60, parts 1 through 4.
- State agency-owned buildings remain under state Department jurisdiction for plan review, permitting, and inspections.
“The local legislative body of a county, city, or town may adopt a building code to apply to the county, city, or town by an ordinance or resolution, as appropriate: (a) adopting a building code; or (b) authorizing the adoption of a building code by administrative action.”
50-60-301. County, city, and town building codes authorized ↗Re-checked Oct 1, 2026
One more reviewed finding on this topic
- General — Montana counties' authority to adopt and enforce building codes and require building-code administration for construction in county areas, including unincorporated areas.
  “The local legislative body of a county, city, or town may adopt a building code to apply to the county, city, or town by an ordinance or resolution, as appropriate: (a) adopting a building code; or (b) authorizing the adoption of a building code by administrative action.”
  50-60-301. County, city, and town building codes authorized, MCA ↗Re-checked Oct 1, 2026

Still unanswered

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

Local zoning — Local zoning in Petroleum County, including the Town of Winnett and unincorporated areas.
Septic inspection — Routine inspection requirements for septic or onsite wastewater systems in Petroleum County.
Off-grid sanitation — Off-grid sanitation systems in Petroleum County, including systems not connected to municipal sewer.

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 Petroleum County, Montana

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

Petroleum County scores 40/100 on the Bolthole Index, a marginal county profile. Its strengths: deep seclusion — about 334 people within 15 miles and low administrative friction for a quiet rural property. Watch-outs: weak self-sufficiency basics: only 14.3″ of rain a year and elevated current hazard exposure.

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

Petroleum County does not require a county building permit for a home in unincorporated areas, and it has no county-wide zoning. Onsite septic is permitted by Montana Department of Environmental Quality. Owner-builders may act as their own contractor to build their home. 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.

Can you live in an RV or tiny home on your land in Petroleum County?

Living in an RV on your own land in Petroleum County is allowed: Unincorporated Petroleum County: no county rule sets this, because Petroleum County's own reviewed answer confirms it has no county-wide zoning ordinance. Septic, floodplain, subdivision and health rules still apply; cities and towns set their own rules inside their limits. The official hazard mitigation plan separately reports that Petroleum County has a Growth Management Ordinance in place; the county growth policy states that a growth policy is not itself a regulation or ordinance. A tiny home is allowed. Confirm with the county before relying on it.

How much does land cost in Petroleum County, Montana?

Land in Petroleum County runs about $1,059 per acre, based on the latest county data.

What is the water situation in Petroleum County?

Petroleum County gets about 14.3" of rain a year, with severe drought in roughly 12.1% of years.

How remote is Petroleum County?

A typical private-land location has about 334 people within 15 miles and 69,424 within 100 miles. These radius catchments are the published fallback where road routing is unavailable.

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

At a glance

Who to call

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

Who issues building permits in Petroleum County, and how do you reach them?

Does Petroleum County, Montana have zoning?

How do septic permits work in Petroleum County?

Can you live in an RV or tiny home on your land in Petroleum County?

How do you build a home in Petroleum County, Montana, step by step?

What should you check before buying land in Petroleum County, Montana?

Watch-outs

Sources

Compared with neighboring counties

Petroleum County in Montana

How Petroleum County scores

Find land. Bring the promising ones back.

Parcel due diligence

Cities and towns in Petroleum County

Answers from the rulebook for Petroleum County

Petroleum County rules

Montana rules that apply here

Still unanswered

Living off-grid in Petroleum County, Montana

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

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

Can you live in an RV or tiny home on your land in Petroleum County?

How much does land cost in Petroleum County, Montana?

What is the water situation in Petroleum County?

How remote is Petroleum County?

How Petroleum compares in Montana