Lemhi County, Idaho
USDA's soil survey flags shrink-swell clay on 10% of Lemhi County's mapped land and a shallow water table under basements on 12%, both below the national shares of 15% and 29%. The soil survey maps 34% of the county's land area; these shares describe the mapped part.
0.3% of the county is in drought on the October 13, 2026 Drought Monitor map, down from 1.3% a week earlier. FEMA's flood data list 5 flood losses here since 2016. 53% of homes were built before 1980, against 50% nationally; the median home dates from 1979.
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 Lemhi County
| Expansive clay (limits slab homes) | 9.7% |
| High water table (limits basements) | 11.8% |
| Septic fields very limited | 88.7% |
| Clay swell (LEP, by area) | 2.7% |
| High-swell land (LEP 6%+) | 10.2% |
| Mapped soil | 1,003,090 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Millhi | 4% | n/a |
| Pahsimeroi | 4% | n/a |
| Dawtonia | 3% | n/a |
| Fritz | 3% | n/a |
| Dacont | 3% | n/a |
| Klug | 3% | n/a |
How we count · survey areas ID752 (2025-08-27), ID758 (2025-08-27)
What the numbers mean here
Rain over the 12 months to August 2026: 21.03 in, 0.24 in above the 1991-2020 average year of 20.79 in.
USDA rates 89% of the land very limited for septic absorption fields.
With shrink-swell clay on 10% and a shallow water table on 12% of the land, the soil survey points to neither problem across most of Lemhi County; conditions still vary lot by lot.
Drought
0.3% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 41 of the last 52 weeks; the most was 100% of its area, in 5 weeks, most recently on the June 23, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 5.4% |
| D1 moderate drought or worse | 0.3% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
5 flood losses since 2016, $109,560 paid. The worst year was 2017, with 3.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 3 |
| 2018 | 0 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 2 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 20.79 in |
| 12 months to August 2026 | 21.03 in (+0.24) |
| 2025 | 21.91 in (+1.12) |
| Wettest year since 1895 | 1911: 29.07 in |
| Driest year since 1895 | 1935: 12.12 in |
| Days with 1 inch or more, normal at SALMON-KSRA (17 mi away) | 0.1 |
Homes
| Housing units | 4,676 |
| Median year built | 1979 |
| Built before 1980 | 53% |
| Built 2000 or later | 18% |
| Owner-occupied | 79% |
| Median value, owner-occupied | $326,100 |
| Single-family detached | 74% |
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 |
|---|---|---|---|
| Custer County, ID | 49 mi | 3% | 7% |
| Beaverhead County, MT | 51 mi | 6% | 9% |
| Ravalli County, MT | 80 mi | under 1% | 8% |
| Valley County, ID | 85 mi | 1% | 14% |
| Clark County, ID | 87 mi | 4% | 4% |
| Deer Lodge County, MT | 88 mi | 6% | 10% |
| Silver Bow County, MT | 90 mi | 2% | 5% |
| Butte County, ID | 93 mi | 1% | 2% |
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