Sweet Grass County, Montana
Shrink-swell clay limits houses without basements on 16% of Sweet Grass County's mapped land, a higher share than 64% of US counties. A shallow water table limits basements on 5%.
69.9% of the county is in drought on the October 13, 2026 Drought Monitor map, down from 85.2% a week earlier. FEMA's flood data list 2 flood losses here since 2016. 51% 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 Sweet Grass County
| Expansive clay (limits slab homes) | 15.9% |
| High water table (limits basements) | 5.0% |
| Septic fields very limited | 76.8% |
| Clay swell (LEP, by area) | 4.0% |
| High-swell land (LEP 6%+) | 17.5% |
| Mapped soil | 1,132,644 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Cabbart | 9% | under 1% |
| Castner | 5% | n/a |
| Cabba | 4% | n/a |
| Rentsac | 3% | n/a |
| Reedpoint | 3% | n/a |
| Delpoint | 3% | n/a |
How we count · survey areas MT623 (2025-08-30), MT639 (2025-08-31), MT640 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 4.0% by land area here, and 17% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 16% of the mapped land.
Clay shrinks as it dries: 69.9% of the county is in drought on the latest map, and 16% of Sweet Grass County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 16.94 in, 2.57 in below the 1991-2020 average year of 19.51 in.
USDA rates 77% of the land very limited for septic absorption fields.
Drought
69.9% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 38 of the last 52 weeks; the most was 100% of its area, in 18 weeks, most recently on the September 22, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 69.9% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
2 flood losses since 2016, $93,110 paid. The worst year was 2022, with 1.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 1 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 1 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 19.51 in |
| 12 months to August 2026 | 16.94 in (-2.57) |
| 2025 | 22.00 in (+2.49) |
| Wettest year since 1895 | 1975: 26.77 in |
| Driest year since 1895 | 1939: 12.59 in |
| Days with 1 inch or more, normal at BIG TIMBER (2 mi away) | 1.9 |
Homes
| Housing units | 1,900 |
| Median year built | 1979 |
| Built before 1980 | 51% |
| Built 2000 or later | 23% |
| Owner-occupied | 80% |
| Median value, owner-occupied | $330,100 |
| Single-family detached | 82% |
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 |
|---|---|---|---|
| Stillwater County, MT | 29 mi | 26% | 5% |
| Park County, MT | 37 mi | 11% | 4% |
| Wheatland County, MT | 48 mi | n/a | n/a |
| Golden Valley County, MT | 55 mi | 26% | 2% |
| Carbon County, MT | 60 mi | 30% | 2% |
| Gallatin County, MT | 62 mi | 9% | 9% |
| Meagher County, MT | 72 mi | n/a | n/a |
| Yellowstone County, MT | 81 mi | 23% | 3% |
Sources: USDA SSURGO (September 2, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status