Building permits, zoning and land rules in Jefferson County, Idaho

Unincorporated Jefferson County requires a building permit for regulated construction, alteration, repair, moving, demolition, occupancy changes and regulated system work¹. Listed minor residential work and structures are exempt, but an exempt structure under 200 square feet still needs a zoning certificate¹. A manufactured home also requires a county building permit before placement⁶.

Unincorporated Jefferson County uses the 2018 International Building Code and International Residential Code, adopted in 2022 with county amendments^5,6. Idaho separately requires permits for electrical, plumbing and HVAC work subject to its state-administered program¹⁰. Give Planning, Zoning & Building the parcel number and project scope before ordering plans². An accessory dwelling unit may be allowed where the zone permits it, with a maximum of 1,200 square feet of living area and 2 bedrooms, plus building, septic, access and inspection requirements¹¹.

Jefferson County Planning, Zoning & Building is the first stop for a project in unincorporated Jefferson County; the office is at 210 Courthouse Way, Suite 170, Rigby, and the phone number is (208) 745-9220². The department manages land use and development exclusively in unincorporated Jefferson County, while its building-permit service also covers Lewisville, Menan and Rigby².

Start through the county's online permit portal by creating and validating an account and uploading the required documents^2,12. Plan-review, GIS and technology fees come before further review, followed by zoning, floodplain and plan review; after approval and final payment, the county issues the permit and the permit sign must be posted¹². Jefferson County publishes a fee schedule, but charges vary by permit type and are set by the Board of County Commissioners⁶. Typical processing is approximately 15 business days for noncommercial applications and 20 business days for commercial applications¹².

Jefferson County zoning applies to unincorporated land; Rigby has its own zoning districts inside city limits^2,3. Eastern Idaho Public Health remains the septic authority throughout Jefferson County⁴. County districts include AG-40, AG-20, AG-10, R-10, R-5, R-1, SN, RR/C, R/O, C-2, C-1, L-I and H-I; uses and dimensional standards vary by district⁶. Ask Planning, Zoning & Building to confirm the parcel's mapped district before purchase².

In agricultural and residential districts, property-line setbacks start at 10 feet for buildings up to 14 feet high and increase with height; measurements extend to projecting roof overhangs, porches or decks⁶. Standard street setbacks are 80 feet from the road centerline, and private-road setbacks are 25 feet from the easement edge; qualifying nonconforming parcels have exceptions⁶. In commercial and industrial districts, the property-line minimum is 0 feet, increasing to 25 feet beside residential districts; street setbacks generally start at 80 feet, with 90 feet required along major roads⁶. Commercial and industrial building heights depend on the specific use and/or fire district approval¹³.

Eastern Idaho Public Health regulates and permits on-site sewage disposal in Jefferson County; its local office is at 380 Community Lane in Rigby and its phone number is (208) 745-7297^4,14. A new, expanded, repaired, replacement, tank-only, central or large-soil-absorption installation requires a septic permit, a scaled or dimensional plot plan, a building plan and a site evaluation by an Environmental Health Specialist⁴. The septic permit is required before obtaining the county building permit⁴.

The permit remains valid for 2 years and may be renewed for $50⁴. A permitted system cannot receive wastewater until the final installation inspection¹⁵. Only 13.3% of Jefferson County soils rate as lacking severe limitations for a conventional drain field, so complete the site evaluation early¹⁶. A septic permit may be denied where public or central wastewater treatment is reasonably accessible¹⁷.

In unincorporated Jefferson County, using an RV as primary living quarters outside a legal RV or manufactured-home park for more than 30 days in a one-year period requires an RV residency permit and a legal parcel of at least 1 acre⁶. Authorization lasts up to 1 year, with a possible 1-year extension for appropriate screening and a compliance inspection after 6 months⁶. An RV used with an open building permit does not need the additional residency permit⁶. The RV needs acceptable wastewater disposal, setbacks and approved skirting; rental use and another occupied RV on the property are prohibited⁶.

Jefferson County includes tiny houses in its RV living-quarters definition under these conditions⁶. We could not confirm a general minimum dwelling size; ask Planning, Zoning & Building to classify the proposed home². Cottage housing developments require a conditional use permit, with cottages containing 400 to 1,600 square feet¹³. Within those developments, cottages and ADUs over garages have a 25-foot height cap, accessory structures have an 18-foot cap, and roof portions above 18 feet need at least a 6:12 pitch¹³.

1. Ask Jefferson County Planning, Zoning & Building to confirm the parcel's mapped district, allowed use, setbacks and dimensional standards⁶.
2. Document the water source and sewer provider, or obtain the applicable Eastern Idaho Public Health authorization and septic permit before applying for the county building permit^4,11.
3. Obtain an Idaho Department of Water Resources drilling permit before drilling a private well⁹.
4. Create the county portal account, upload the plans and documents, and pay the initial review fees¹².
5. Complete zoning, floodplain and plan review, pay the remaining fees, receive the permit and post its sign¹².
6. Obtain the required electrical, plumbing and HVAC permits for regulated trade work¹⁰.
7. Pass required final inspections; Jefferson County does not issue the applicable certificate of occupancy or completion until failed items are corrected and reinspected¹².

Jefferson County's residential minimum lot sizes vary by zoning district from 1 to 40 acres, with exceptions including smaller clustered lots and qualifying Suburban Neighborhood lots served by community sewer and water⁶. Development in regulated unincorporated Jefferson County floodplain areas requires a floodplain development permit; the county ADU application also calls for an elevation certificate for floodplain construction^11,18.

For a private well, Idaho requires a drilling permit and a licensed well driller before construction⁹. If access connects to an Idaho state highway, an Idaho Transportation Department encroachment permit is required for the driveway or street approach¹⁹. Jefferson County's effective property-tax rate is about 0.5%, with a median annual bill of about $1,775¹⁶. Confirm that the parcel and any proposed division comply with county subdivision rules before relying on a seller's description⁶. A short-term rental of fewer than 30 consecutive days is a residential zoning use and must occupy a structure designed for a single-family household⁶.