St. Clair County, Missouri
A shallow water table limits basements on 33% of St. Clair County's mapped land, a higher share than 52% of US counties. Shrink-swell clay limits houses without basements on 23%.
100% 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. 53% 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 St. Clair County
| Expansive clay (limits slab homes) | 22.5% |
| High water table (limits basements) | 33.4% |
| Septic fields very limited | 93.7% |
| Clay swell (LEP, by area) | 3.9% |
| High-swell land (LEP 6%+) | 14.1% |
| Mapped soil | 448,838 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Goss | 13% | 0% |
| Barden | 11% | n/a |
| Barco | 10% | n/a |
| Hector | 9% | n/a |
| Bolivar | 7% | n/a |
| Deepwater | 5% | n/a |
How we count · survey areas MO185 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 3.9% by land area here, and 14% 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: 100% of the county is in drought on the latest map, and 23% of St. Clair County's mapped land has shrink-swell clay.
On 33% of St. Clair 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: 43.71 in, 0.09 in below the 1991-2020 average year of 43.80 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 25 of the last 52 weeks; the most was 100% of its area, in 13 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 | 31.2% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in St. Clair County since 2016.
Rain
| Average year, 1991-2020 | 43.80 in |
| 12 months to August 2026 | 43.71 in (-0.09) |
| 2025 | 38.55 in (-5.25) |
| Wettest year since 1895 | 1951: 62.23 in |
| Driest year since 1895 | 1980: 23.45 in |
| Days with 1 inch or more, normal at OSCEOLA (4 mi away) | 13.9 |
Homes
| Housing units | 5,290 |
| Median year built | 1979 |
| Built before 1980 | 53% |
| Built 2000 or later | 19% |
| Owner-occupied | 76% |
| Median value, owner-occupied | $157,100 |
| Single-family detached | 74% |
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 |
|---|---|---|---|
| Cedar County, MO | 22 mi | 11% | 49% |
| Henry County, MO | 24 mi | 34% | 60% |
| Hickory County, MO | 26 mi | 51% | 26% |
| Benton County, MO | 32 mi | 41% | 28% |
| Vernon County, MO | 33 mi | 54% | 63% |
| Bates County, MO | 34 mi | 70% | 75% |
| Polk County, MO | 36 mi | 24% | 59% |
| Dade County, MO | 42 mi | 17% | 45% |
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