Building permits, zoning and septic rules in Lewis and Clark County, Montana

At a glance

Building permit

Not required for a single-family home in unincorporated Lewis and Clark County¹

State building permit exemption

Residential buildings with fewer than five dwelling units are exempt unless they serve transient guests²

Zoning

Only inside designated Part 1 and Part 2 zoning districts - check the county's interactive map for your parcel³⁴

Septic permits

Issued by Lewis and Clark Public Health's Environmental Services Division after a site evaluation⁵⁶

Minimum home size

Not regulated by the county's zoning rules⁴

Subdivision review

A pre-application meeting is required for a proposed subdivision⁷

Driveway on a state highway

Needs a separate Montana Department of Transportation approach permit⁸

Owner-builder plumbing

No state plumbing permit if you do the work yourself in your own non-rental home⁹

Private well

Water-right exception for up to 35 gallons per minute and 10 acre-feet per year; larger use needs a water permit¹⁰¹¹

Who to call

Contact details are copied from each office’s official page and were checked against it on October 10, 2026.

Do you need a building permit in Lewis and Clark County, Montana?

No. Lewis and Clark County has no residential building-permit program of its own for unincorporated land; the county's Community Development and Planning Department handles zoning, subdivision review and floodplain review instead of building codes¹. Montana's state permit exempts residential buildings with fewer than five dwelling units unless they serve transient guests, along with farm and ranch buildings and qualifying private garages and storage buildings². Covered projects must receive the state building permit before construction begins and before required plumbing, mechanical or electrical permits are issued². The state exemption applies outside certified local-government program areas; Helena is a certified local government limited to city limits, and the rest of the county falls under the State Building Codes Bureau¹². A homeowner who does their own plumbing in a personal-use, non-rental home needs no plumbing permit⁹. Montana's contractor-registration exemption for an owner working on their own property does not waive building, septic or other permits¹³.

Who handles building-related permits in Lewis and Clark County, and how do you reach them?

Since there is no county building department, your main point of contact for land-use questions is the Lewis and Clark County Community Development and Planning Department, which coordinates zoning, subdivision review, floodplain development, open lands and historic preservation¹⁴. Reach the department at 406-447-8374, or visit the City-County Building at 316 N. Park Ave., Room 230, Helena, MT 59623, Monday through Friday from 8:00 am to 5:00 pm¹⁴. Montana's Building Codes Program handles projects that require a state building permit, and the permit holder must notify the inspector when covered work is ready and provide access for required inspections¹⁵. Ask the Planning Department about floodplain review and subdivision review before finalizing the site plan¹⁴.

Does Lewis and Clark County have zoning, and what does it mean for RVs, tiny homes and setbacks?

Zoning is not countywide: Lewis and Clark County uses Part 1 and Part 2 zoning, and only parcels inside an established district are zoned³⁴. Part 2 regulations cover the Helena Valley and the Fort Harrison rural and urban growth areas, while the county has several Part 1 districts⁴. Use the county's interactive mapping site to identify the parcel's district before planning around setbacks or uses⁴. The county's zoning regulations do not set a minimum size or price for houses⁴. We could not confirm a countywide RV- or tiny-home occupancy rule, so ask the Planning Department what applies to the parcel¹⁴.

How do septic and well permits work in Lewis and Clark County?

Septic systems in unincorporated Lewis and Clark County are permitted by the county's Environmental Services Division, part of Lewis and Clark Public Health, at their office in the Murray Building on Ninth Avenue in Helena⁶. Before you can get a septic permit you generally need a site evaluation of the soils, topography and water quality on your parcel, unless you already hold a DEQ subdivision approval or a previous site approval that still meets current regulations⁶. Site evaluation fees run $480 for a new site including the required non-degradation review, $400 for a replacement system or review of an existing system, and $80 for an individual non-degradation review alone, and the county has up to 20 working days to approve or deny the evaluation⁶. Once you have an approved site evaluation, permit fees depend on the system and installer: a certified installer pays $160 for a standard gravity system versus $320 for a non-certified installer, and only certified installers may install a pressure-dosed system at $320, an individual engineered system at $480, or a multi-user/public system at $720; a septic tank permit is $80 and a holding tank permit is $160 regardless of installer⁶. Start construction before your permit is issued and the fee doubles, with possible added penalties, and once issued a permit expires one year from the date it was granted⁶. The county permits individual septic tanks with drain fields, community treatment systems, holding tanks and outhouses¹⁶. Even if your subdivision already has a Montana DEQ Certificate of Subdivision Approval, that certificate does not replace the county's drainfield permit, so you still need one¹⁷⁶. For a private well, a new groundwater use of 35 gallons per minute or less and no more than 10 acre-feet a year can qualify for a permit exception instead of a water permit, while larger uses need a DNRC water permit¹⁰¹¹.

Can you live in an RV or tiny home on your land in Lewis and Clark County?

We could not confirm a countywide rule for living in an RV or tiny home on private land in unincorporated Lewis and Clark County. Zoning applies only inside designated Part 1 and Part 2 districts, so check the county's interactive map and ask the Community Development and Planning Department what applies to the parcel³⁴¹⁴. A residential structure that needs wastewater disposal and is not connected to municipal sewer requires a county septic permit⁶. A land division that creates qualifying RV or mobile-home rental spaces can also trigger county subdivision review⁷.

How do you build a home in Lewis and Clark County, step by step?

1. Check the county's interactive map and ask Community Development and Planning what the parcel's zoning and floodplain status allow⁴¹⁴.
2. If the project divides land into qualifying parcels or creates multiple RV or mobile-home rental spaces, schedule the required subdivision pre-application meeting before applying⁷.
3. Order a septic site evaluation unless the parcel has a qualifying DEQ subdivision approval or prior site approval; the county may take up to 20 working days⁶.
4. Arrange a test hole, obtain a nearby well-water sample if required, and prepare a general facilities plan for the site evaluation⁶.
5. Confirm that the home fits the state exemption; covered projects need a state building permit before construction and before required trade permits².
6. If a state permit is required, notify the inspector when work is ready and provide access for required inspections¹⁵.
7. Obtain an MDT approach permit or right-of-way agreement before building a new or modified driveway onto a state highway⁸.
8. If any part of the parcel may be in a flood zone, ask the local floodplain administrator whether a floodplain development permit is needed before fill, excavation or new construction¹⁸.
9. Obtain the septic permit before any construction, including well drilling or foundation excavation, to avoid a doubled fee and possible penalties⁶.

What should you check before buying land in Lewis and Clark County, Montana?

Ask Lewis and Clark Public Health's Environmental Services Division about a site evaluation before you commit to a parcel: only about 7.2% of the county's soils are rated free of severe limitations for a conventional septic drain field, and sites with shallow groundwater or bedrock face extra restrictions, since state and local rules require at least 4 feet of separation between a drain field trench and both the water table and bedrock¹⁹⁶. Check the county's interactive zoning map, since zoning in Lewis and Clark County only applies inside established Part 1 and Part 2 districts and rules differ sharply where it does apply⁴. About 51.1% of the county is federal land, which affects both access and what is actually available to buy²⁰. Only 26.8% of the county's land sits at 15% slope or gentler, so ask about slope and access before you assume a building site will be easy to grade²¹. Confirm how your access road connects: a new or modified driveway onto a state highway needs a Montana Department of Transportation approach permit or right-of-way agreement, while a driveway onto a county road is a local matter to confirm with the county⁸. Lewis and Clark County's median property tax bill is about $2,886 a year at an effective rate near 0.8%, and typical homes in the county are valued around $471,902²²²³²⁴.

Watch-outs

• Land divisions creating qualifying parcels under 160 acres, condominiums, or multiple RV or mobile-home rental spaces require subdivision review, including a pre-application meeting; lots cannot be transferred until final approval and recording⁷.
• Starting septic construction before your permit is issued doubles the permit fee and may add penalties, and a septic permit expires one year after it is issued, so time your application to your construction schedule⁶.

Sources

1. Montana DLI Building Codes - Is a State Building Permit Needed? (2026 county census)
2. Building Permits, quoted and re-checked
3. Lewis & Clark County - Zoning (2026 county census)
4. Lewis and Clark County Zoning (Community Development and Planning) (lccountymt.gov)
5. Septic System Programs (2026 county census)
6. Lewis and Clark Public Health - Environmental Services Division (lccountymt.gov)
7. Subdivision Review, quoted and re-checked
8. Approach Manual for Landowners and Developers (Montana statewide rule), quoted and re-checked
9. Plumbing Permits, quoted and re-checked
10. Exempt Well Updates and Information (Montana statewide rule), quoted and re-checked
11. Exempt Well Updates and Information (Montana statewide rule), quoted and re-checked
12. Certified City, County and Town Programs, quoted and re-checked
13. MCA -- December 2025: Chapter 45 Construction Contractors, quoted and re-checked
14. Lewis and Clark County Community Development and Planning Department (lccountymt.gov)
15. Building Permits, quoted and re-checked
16. Septic System Programs, quoted and re-checked
17. Engineering Infrastructure & Subdivisions (Montana statewide rule), quoted and re-checked
18. Stream Permitting (Montana statewide rule), quoted and re-checked
19. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
20. Federal land share: Bolthole Index county data
21. Share of land at 15% slope or less: Bolthole Index county data
22. Median property tax bill: Bolthole Index county data
23. Effective property tax rate: Bolthole Index county data
24. Typical home value (Zillow): Bolthole Index county data

Written October 10, 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.