Big Horn County, Montana
Shrink-swell clay limits houses without basements on 30% of Big Horn County's mapped land, a higher share than 80% of US counties. A shallow water table limits basements on 1%.
89.4% 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. 59% of homes were built before 1980, against 50% nationally; the median home dates from 1976.
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 Big Horn County
| Expansive clay (limits slab homes) | 29.8% |
| High water table (limits basements) | 0.7% |
| Septic fields very limited | 77.8% |
| Clay swell (LEP, by area) | 4.4% |
| High-swell land (LEP 6%+) | 30.0% |
| Mapped soil | 4,457,112 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Yamacall | 6% | n/a |
| Cabbart | 4% | under 1% |
| Delpoint | 4% | n/a |
| Midway | 4% | n/a |
| Lismas | 3% | n/a |
| Duncom | 3% | n/a |
How we count · survey areas MT607 (2025-08-30), MT649 (2025-09-03)
What the numbers mean here
Clay swell averages a linear extensibility of 4.4% by land area here, and 30% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 30% of the mapped land.
Clay shrinks as it dries: 89.4% of the county is in drought on the latest map, and 30% of Big Horn County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 15.75 in, 0.18 in below the 1991-2020 average year of 15.93 in.
USDA rates 78% of the land very limited for septic absorption fields.
Drought
89.4% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 37 of the last 52 weeks; the most was 100% of its area, in 20 weeks, most recently on the September 29, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 98.7% |
| D1 moderate drought or worse | 89.4% |
| D2 severe or worse | 40.6% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Big Horn County since 2016.
Rain
| Average year, 1991-2020 | 15.93 in |
| 12 months to August 2026 | 15.75 in (-0.18) |
| 2025 | 20.55 in (+4.62) |
| Wettest year since 1895 | 1978: 24.20 in |
| Driest year since 1895 | 2012: 8.67 in |
| Days with 1 inch or more, normal at YELLOWTAIL DAM (21 mi away) | 2.7 |
Homes
| Housing units | 4,527 |
| Median year built | 1976 |
| Built before 1980 | 59% |
| Built 2000 or later | 14% |
| Owner-occupied | 67% |
| Median value, owner-occupied | $143,400 |
| Single-family detached | 69% |
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 |
|---|---|---|---|
| Yellowstone County, MT | 52 mi | 23% | 3% |
| Sheridan County, WY | 53 mi | 21% | 1% |
| Treasure County, MT | 58 mi | 44% | 4% |
| Big Horn County, WY | 65 mi | 12% | 4% |
| Rosebud County, MT | 67 mi | 25% | under 1% |
| Carbon County, MT | 74 mi | 30% | 2% |
| Musselshell County, MT | 88 mi | 24% | 1% |
| Stillwater County, MT | 92 mi | 26% | 5% |
Sources: USDA SSURGO (September 3, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status