Off-Grid Living in Carbon County, Montana

Carbon County, Montana is one of those places where the rules aren't a simple "yes" or "no," so let me walk you through what I found while researching this for Live Off The Grid.

First, understand the framework here: Carbon County doesn't have traditional Euclidean zoning. Instead, the county operates under countywide Development Regulations and Subdivision Regulations, administered by a County Planning Board (which serves as the county's zoning commission under Montana Code Annotated 76-2-220) and a Planning Director. That's a meaningful distinction if you're used to thinking in terms of "zoning districts."

On raw land occupancy, subdividing land for sale, rent, or lease under 160 acres triggers county subdivision review, and any parcel under 20 acres also needs state DEQ sanitation review, per the Montana Subdivision and Platting Act. If you're just occupying land you already own without subdividing it, I didn't find anything in county materials that separately prohibits that.

For dwellings, tiny homes, and RVs, the county's Development Regulations draw a real line between manufactured/mobile homes (which have their own standards, including minimum lot area in mobile home parks) and site-built or modular units built to Uniform Building Code standards. Montana's statewide Appendix Q applies to foundation-built tiny homes, while tiny homes on wheels generally get treated like RVs, restricted to RV parks and campgrounds. I couldn't confirm whether Carbon County layers on any additional tiny-house-specific rule beyond that.

Building permits for single-family homes are the murkiest piece. Montana exempts most single-family residential construction from state building codes unless a county opts in, and I could not confirm from the county's own site whether Carbon County has opted into IRC-based permitting for standalone homes outside the development-permit process. Call the Planning Office directly before you build.

Septic is handled by Carbon County Environmental Health. Parcels over 20 acres (not counting road frontage) only need a county-issued Construction Authorization. Smaller parcels need DEQ involvement first, then a county authorization and inspection before a Permit to Operate is issued. Composting toilets aren't addressed in what I found.

Greywater and rainwater harvesting have no county-specific rules I could locate, so both fall back to whatever the state framework allows or doesn't restrict. Private wells can use Montana's exempt-well track through DNRC, and if your well is tied to a septic permit, expect coliform and nitrate testing requirements from state DPHHS. Living fully off-grid, disconnected from utilities, isn't explicitly addressed in any ordinance I found, though development permit conditions on new subdivided lots could indirectly affect your options.

Bottom line: call before you commit to a plan.