Custer County, Idaho
USDA's soil survey flags shrink-swell clay on 3% of Custer County's mapped land and a shallow water table under basements on 7%, both below the national shares of 15% and 29%. The soil survey maps 33% of the county's land area; these shares describe the mapped part.
3.4% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 42% of homes were built before 1980, against 50% nationally; the median home dates from 1986.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Custer County
| Expansive clay (limits slab homes) | 2.9% |
| High water table (limits basements) | 6.5% |
| Septic fields very limited | 85.0% |
| Clay swell (LEP, by area) | 2.1% |
| High-swell land (LEP 6%+) | 3.2% |
| Mapped soil | 1,050,448 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Dawtonia | 5% | n/a |
| Zeebar | 4% | n/a |
| Dacont | 4% | n/a |
| Zer | 3% | n/a |
| Donkehill | 3% | n/a |
| Snowslide | 3% | n/a |
How we count · survey areas ID752 (2025-08-27)
What the numbers mean here
Rain over the 12 months to August 2026: 23.20 in, 1.25 in above the 1991-2020 average year of 21.95 in.
USDA rates 85% of the land very limited for septic absorption fields.
With shrink-swell clay on 3% and a shallow water table on 7% of the land, the soil survey points to neither problem across most of Custer County; conditions still vary lot by lot.
Drought
3.4% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 39 of the last 52 weeks; the most was 100% of its area, in 4 weeks, most recently on the June 23, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 39.7% |
| D1 moderate drought or worse | 3.4% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Custer County since 2016.
Rain
| Average year, 1991-2020 | 21.95 in |
| 12 months to August 2026 | 23.20 in (+1.25) |
| 2025 | 25.20 in (+3.25) |
| Wettest year since 1895 | 1995: 32.28 in |
| Driest year since 1895 | 1924: 13.69 in |
| Days with 1 inch or more, normal at CHILLY BARTON FLAT (29 mi away) | 0.1 |
Homes
| Housing units | 3,137 |
| Median year built | 1986 |
| Built before 1980 | 42% |
| Built 2000 or later | 22% |
| Owner-occupied | 77% |
| Median value, owner-occupied | $381,700 |
| Single-family detached | 70% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Lemhi County, ID | 49 mi | 10% | 12% |
| Camas County, ID | 59 mi | 19% | 22% |
| Blaine County, ID | 63 mi | 11% | 4% |
| Butte County, ID | 67 mi | 1% | 2% |
| Boise County, ID | 75 mi | 3% | 2% |
| Valley County, ID | 78 mi | 1% | 14% |
| Elmore County, ID | 86 mi | 7% | 2% |
| Lincoln County, ID | 89 mi | 16% | 1% |
Sources: USDA SSURGO (August 27, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status