Lake County, Montana
USDA's soil survey flags shrink-swell clay on 2% of Lake County's mapped land and a shallow water table under basements on 3%, both below the national shares of 15% and 29%. None 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. 43% 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 Lake County
| Expansive clay (limits slab homes) | 2.0% |
| High water table (limits basements) | 3.4% |
| Septic fields very limited | 70.0% |
| Clay swell (LEP, by area) | 2.3% |
| High-swell land (LEP 6%+) | 0.5% |
| Mapped soil | 1,047,456 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Bigarm | 4% | n/a |
| Post | 3% | n/a |
| Finleypoint | 3% | n/a |
| Round Butte | 3% | n/a |
| Niarada | 3% | n/a |
| Courville | 2% | n/a |
How we count · survey areas MT606 (2025-08-29), MT619 (2025-08-30), MT629 (2025-08-30), MT633 (2025-08-30)
What the numbers mean here
Rain over the 12 months to August 2026: 29.58 in, 4.75 in above the 1991-2020 average year of 24.83 in.
USDA rates 70% of the land very limited for septic absorption fields.
With shrink-swell clay on 2% and a shallow water table on 3% of the land, the soil survey points to neither problem across most of Lake County; conditions still vary lot by lot.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 16 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the December 2, 2025 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 6.4% |
| D1 moderate drought or worse | 0% |
| 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 Lake County since 2016.
Rain
| Average year, 1991-2020 | 24.83 in |
| 12 months to August 2026 | 29.58 in (+4.75) |
| 2025 | 27.50 in (+2.67) |
| Wettest year since 1895 | 1897: 36.37 in |
| Driest year since 1895 | 1931: 16.32 in |
| Days with 1 inch or more, normal at SKQ DAM (8 mi away) | 0.9 |
Homes
| Housing units | 16,468 |
| Median year built | 1986 |
| Built before 1980 | 43% |
| Built 2000 or later | 26% |
| Owner-occupied | 75% |
| Median value, owner-occupied | $421,800 |
| Single-family detached | 78% |
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 |
|---|---|---|---|
| Missoula County, MT | 43 mi | 1% | 3% |
| Flathead County, MT | 45 mi | 1% | 3% |
| Sanders County, MT | 52 mi | 2% | 3% |
| Mineral County, MT | 59 mi | under 1% | 4% |
| Powell County, MT | 77 mi | 10% | 6% |
| Teton County, MT | 85 mi | 23% | 8% |
| Shoshone County, ID | 87 mi | under 1% | 4% |
| Lewis and Clark County, MT | 87 mi | 6% | 3% |
Sources: USDA SSURGO (August 30, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status