Washington County, Missouri
Shrink-swell clay limits houses without basements on 27% of Washington County's mapped land, a higher share than 78% of US counties. A shallow water table limits basements on 25%.
100% of the county is in drought on the October 13, 2026 Drought Monitor map, up from 73.3% a week earlier. 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 1985.
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 Washington County
| Expansive clay (limits slab homes) | 27.4% |
| High water table (limits basements) | 25.4% |
| Septic fields very limited | 94.1% |
| Clay swell (LEP, by area) | 4.5% |
| High-swell land (LEP 6%+) | 29.0% |
| Mapped soil | 488,148 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Goss | 14% | 1% |
| Sonsac | 13% | n/a |
| Alred | 12% | n/a |
| Rueter | 10% | n/a |
| Gravois | 6% | n/a |
| Cedargap | 5% | n/a |
How we count · survey areas MO221 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 4.5% by land area here, and 29% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 27% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 27% of Washington County's mapped land has shrink-swell clay.
On 25% of Washington County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 42.75 in, 2.81 in below the 1991-2020 average year of 45.56 in.
USDA rates 94% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 23 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 8.4% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Washington County since 2016.
Rain
| Average year, 1991-2020 | 45.56 in |
| 12 months to August 2026 | 42.75 in (-2.81) |
| 2025 | 43.45 in (-2.11) |
| Wettest year since 1895 | 1993: 61.97 in |
| Driest year since 1895 | 1953: 23.15 in |
| Days with 1 inch or more, normal at POTOSI 4 SW (4 mi away) | 12.5 |
Homes
| Housing units | 10,734 |
| Median year built | 1985 |
| Built before 1980 | 43% |
| Built 2000 or later | 23% |
| Owner-occupied | 78% |
| Median value, owner-occupied | $129,400 |
| Single-family detached | 67% |
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 |
|---|---|---|---|
| Crawford County, MO | 23 mi | 15% | 34% |
| Iron County, MO | 24 mi | 8% | 42% |
| St. Francois County, MO | 25 mi | 15% | 40% |
| Jefferson County, MO | 29 mi | 37% | 34% |
| Franklin County, MO | 34 mi | 14% | 61% |
| Dent County, MO | 40 mi | 1% | 44% |
| Reynolds County, MO | 40 mi | 7% | 22% |
| Ste. Genevieve County, MO | 40 mi | 16% | 34% |
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