Yellowstone County, Montana
Shrink-swell clay limits houses without basements on 23% of Yellowstone County's mapped land, a higher share than 74% of US counties. A shallow water table limits basements on 3%.
7.5% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 46 flood losses here since 2016, 47% of them in buildings with basements. 48% of homes were built before 1980, against 50% nationally; the median home dates from 1982.
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 Yellowstone County
| Expansive clay (limits slab homes) | 23.4% |
| High water table (limits basements) | 2.5% |
| Septic fields very limited | 73.3% |
| Clay swell (LEP, by area) | 4.5% |
| High-swell land (LEP 6%+) | 33.6% |
| Mapped soil | 1,639,305 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Cabbart | 9% | under 1% |
| Bainville | 9% | n/a |
| Lismas | 7% | n/a |
| McRae | 7% | n/a |
| Blacksheep | 5% | n/a |
| Delpoint | 5% | n/a |
How we count · survey areas MT111 (2025-08-29)
What the numbers mean here
Clay swell averages a linear extensibility of 4.5% by land area here, and 34% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 23% of the mapped land.
Clay shrinks as it dries: 7.5% of the county is in drought on the latest map, and 23% of Yellowstone County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 13.37 in, 1.23 in below the 1991-2020 average year of 14.60 in.
USDA rates 73% of the land very limited for septic absorption fields.
Drought
7.5% 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 | 26.7% |
| D1 moderate drought or worse | 7.5% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
46 flood losses since 2016, $1.0 million paid. The worst year was 2022, with 25. Foundations of the buildings, where recorded: 47% basements, 18% slabs, 24% crawl spaces, 11% elevated. Median water depth outside the building: 10 in.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 1 |
| 2018 | 12 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 25 |
| 2023 | 7 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 14.60 in |
| 12 months to August 2026 | 13.37 in (-1.23) |
| 2025 | 19.16 in (+4.56) |
| Wettest year since 1895 | 1978: 23.46 in |
| Driest year since 1895 | 1931: 7.22 in |
| Days with 1 inch or more, normal at HUNTLEY EXP STN (2 mi away) | 1.4 |
Homes
| Housing units | 74,239 |
| Median year built | 1982 |
| Built before 1980 | 48% |
| Built 2000 or later | 28% |
| Owner-occupied | 70% |
| Median value, owner-occupied | $349,500 |
| Single-family detached | 65% |
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 |
|---|---|---|---|
| Musselshell County, MT | 40 mi | 24% | 1% |
| Big Horn County, MT | 52 mi | 30% | 1% |
| Treasure County, MT | 52 mi | 44% | 4% |
| Golden Valley County, MT | 53 mi | 26% | 2% |
| Stillwater County, MT | 57 mi | 26% | 5% |
| Carbon County, MT | 61 mi | 30% | 2% |
| Rosebud County, MT | 79 mi | 25% | under 1% |
| Sweet Grass County, MT | 81 mi | 16% | 5% |
Sources: USDA SSURGO (August 29, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status