Building permits, zoning and septic rules in Yellowstone County, Montana

Not from the county, for a structure outside the city limits of Billings: Yellowstone County does not issue building permits or certificates of occupancy there¹. Inside Billings, the city's permit rules apply, and the county notice says outside structures are not subject to the same restrictions¹. Montana law also exempts residential buildings with fewer than five dwelling units, farm and ranch buildings, and private garages and storage buildings from the state building permit in areas outside certified cities, though separate electrical, plumbing or mechanical permits may still apply⁹. Skipping a building permit does not skip the other approvals: unincorporated land still needs a zoning permit from the Planning Division, a septic permit from RiverStone Health if there is no sewer, a driveway approach permit where access meets a county road, and a floodplain permit if the parcel is in a mapped flood zone^2,4,10,11.

Zoning for unincorporated Yellowstone County runs through the City-County Planning Division, a joint agency with the City of Billings, at (406) 657-8247, 316 N. 26th Street, Billings, MT 59101, or through its CityView online portal². The division "provides community planning and development services to Yellowstone County, the City of Billings, and the Town of Broadview."² Floodplain permits and determinations come from Yellowstone County's Floodplain Administration (Public Works) at 406-256-2735 or pubworks@yellowstonecountymt.gov¹¹. The Public Works Department also issues approach permits for driveways onto county-managed roads; construction may not begin until the permit issues, and a residential access permit is $75^1,10. Septic permits come from RiverStone Health Environmental Health Services at 406.256.2770, 123 South 27th Street, Billings, MT 59101⁴.

Yes. Unincorporated Yellowstone County has a County Zoning Code and Zoning Regulations, administered with the City-County Planning Division and the Zoning Commission^2,7. The county's map service shows separate Billings, Broadview and Laurel zoning layers, so a parcel inside one of those towns follows that town's zoning, not the county's³. The Planning Division reviews "proposed projects and processing subdivision applications, applications for requests for zoning changes and variances, and special use permits" for the county². We could not confirm district-by-district lot sizes, setbacks or height limits from the county's zoning code, so ask the Planning Division which district covers the parcel before you buy or build⁷.

Septic systems in Yellowstone County are permitted by RiverStone Health, not the county government⁴. The review path depends on lot size: parcels under 20 acres go through the Montana Department of Environmental Quality review, and parcels of 20 acres or more go through local review⁴. Before RiverStone Health reviews the lot, the applicant obtains a Permit Tracking Sheet from the Yellowstone County Courthouse, Room 305, which verifies an assigned address, an issued approach permit, and that the property is not in a floodplain⁴. The application also needs a detailed lot layout, the required fee and, for a residence, the bedroom count⁴. New and repaired systems must be inspected and permitted before use, so call 406.256.2770 at installation to schedule the inspection⁴. Only about 19.1% of the county's soils are rated free of severe limits for a conventional drain field, so budget for a site evaluation⁵.

We could not confirm a specific county rule for RV or tiny-home living on a private unincorporated lot, because the zoning code's use and dimensional standards were not available to us; ask the City-County Planning Division which district covers your parcel and whether it allows RV or manufactured-home occupancy^2,7. Where a county has established zoning, Montana law requires that zoning to allow at least one accessory dwelling unit by right on a lot with a single-family dwelling, attached, detached or internal, with a one-time review fee of up to $250¹². Building codes, fire codes and health rules, including septic, still apply to that unit¹². Montana's camping limits of 7 nights per 30-day period apply to Fish, Wildlife & Parks public-use sites, not to your own land¹³.

1. Confirm with the City-County Planning Division that your parcel is outside Billings, Broadview and Laurel and that its zoning district allows the home you plan to build^2,3.
2. Ask the Floodplain Office, using the parcel's legal description, whether a floodplain permit is needed; a non-refundable $50 fee applies to each permit or variance application^11,14.
3. For a driveway onto a county road, get an approach permit from Public Works before building it; for a state highway, apply to the Montana Department of Transportation^10,15.
4. Obtain a Permit Tracking Sheet from the Yellowstone County Courthouse, Room 305⁴.
5. Submit the tracking sheet, lot layout, fee and bedroom count to RiverStone Health for septic approval⁴.
6. Build; no county building permit applies outside Billings, but ask about state electrical, plumbing and mechanical permits^1,9.
7. Call RiverStone Health to schedule the septic inspection before the system is placed into use⁴.

Confirm your parcel's zoning district and any use restrictions with the City-County Planning Division, since the county has zoning even though it skips a county building permit^1,2,7. Check with the Floodplain Administration whether the parcel sits in a mapped Special Flood Hazard Area; Yellowstone County is currently updating its floodplain regulations, so ask what's changing before you close¹¹. Budget for septic due diligence: with only about 19.1% of soils rated free of severe limits for a conventional drain field, a site evaluation should come before you finalize your build plan⁵. The county gets only about 14.6 inches of precipitation a year and sees severe drought in roughly 12.3% of years, so plan your water supply and any well with that dryness in mind⁵. Typical property tax runs about a 0.8% effective rate with a median bill near $2,669 a year, and a typical homeowner's insurance premium runs closer to $2,302 a year, both worth building into your budget⁵.