Custer County, ID zoning map, flood zone and property lines by address
Free, no account. Or open the Idaho map and tap a lot.
Towns in Custer County: Challis.
Flood zone by address
ParcelSheet reads FEMA's National Flood Hazard Layer at the lot: the zone, whether it is a high risk area where lenders ask for flood insurance, and the base flood elevation where FEMA lists one. FEMA has 28 FIRM panels covering Custer County, the newest effective February 2019; no coastal V zones are mapped in it.
The official panel and any Letter of Map Amendment are at FEMA's Map Service Center. An elevation certificate for a Custer house comes from a licensed surveyor and is often on file with the county or city building office.
Property lines
The parcel outline, parcel number and mapped size come from the State of Idaho public parcels, from counties that share them, so a Custer lot shows the same lines the county assessor draws. Custer County covers about 3,150,193 acres of land and 10,509 acres of water.
Mapped lines are approximate. The Custer County assessor keeps the parcel record (Custer County website); a licensed surveyor sets the true corners.
Zoning
Custer County zones its unincorporated land, and Challis zones the land inside its limits. ParcelSheet shows the use the county assessor lists for the lot and links the county planning and zoning office for the district, the uses it allows and the lot size it needs.
ADU and guest houses
Under Idaho's Local Land Use Planning Act (Idaho Code Title 67, Chapter 65), local governments can allow an accessory dwelling unit on a lot with a house. Whether a Custer lot can add one depends on its district; the county planning and zoning office has the rule. ParcelSheet shows the mapped lot size and the ground's slope, the first two things the question turns on.
Septic and soil
ParcelSheet reads the USDA soil survey at the lot: the soil's name, its septic absorption rating and whether it is prime farmland. Custer County is soil survey area ID752, Custer-Lemhi Area, Idaho, Parts of Blaine, Custer, and Lemhi Counties, last updated August 2026, on Web Soil Survey.
A new or changed septic system in Custer County needs a permit from the public health district that serves Custer County (under Idaho Department of Environmental Quality rules).
Setbacks
Setbacks in Custer County come from the zoning district: the front, side and rear distances a house must keep. ParcelSheet does not draw setback lines; the county zoning office gives them for the lot's district, and Challis for land inside its limits.
Hazards that apply
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a Custer lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in Custer County?
Type the address in the box above and ParcelSheet reads FEMA's flood zone at the lot's center. FEMA has 28 flood map panels covering Custer County, the newest effective February 2019. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in Custer County?
Open the Idaho map, type the address, and the parcel outline from the Custer County assessor shows on the map with its parcel number and mapped size. Mapped lines are approximate; only a licensed surveyor sets the true corners.
What is my property zoned in Custer County?
Zoning in Custer County is set by the county for unincorporated land and by each city (such as Challis) inside its own limits. ParcelSheet shows the use code the county assessor lists and links the office that sets the zoning; the planning office has the final word.
Can I build an ADU in Custer County?
Under Idaho's Local Land Use Planning Act (Idaho Code Title 67, Chapter 65), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In Custer County ask the zoning office for the lot's district first; ParcelSheet shows the lot size as mapped so you can see the room you have.
Do I need a septic permit in Custer County?
Yes. A new or changed septic system in Custer County needs a permit from the public health district that serves Custer County (under Idaho Department of Environmental Quality rules). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area ID752 (Custer-Lemhi Area, Idaho, Parts of Blaine, Custer, and Lemhi Counties).
What can I build on 5 acres in Custer County?
Zoning in Custer County is set by the county for unincorporated land and each city inside its own limits (such as Challis). The zoning district decides the uses, how many homes and the smallest lot it allows on 5 acres. ParcelSheet shows the lot size as mapped and the use code on the parcel record; the planning office has the district and its rules. See the Custer County website.
What are the residential setbacks in Custer County (2026)?
Setbacks in Custer County come from the zoning code of the county, or of the city when the lot is inside city limits: the front, side and rear distances depend on the lot's district. ParcelSheet does not draw setback lines or give a number it did not read; the zoning office gives them for the district. See the Custer County website.
Next to Custer County: Blaine County, Boise County, Butte County, Elmore County, Lemhi County, Valley County.
The Idaho map · All Idaho counties · Flood zones explained · FIRM panels and LOMAs · All 50 states