Jefferson County, Missouri
Shrink-swell clay limits houses without basements on 37% of Jefferson County's mapped land, a higher share than 85% of US counties. A shallow water table limits basements on 34%.
34.6% of the county is in drought on the October 13, 2026 Drought Monitor map, up from 2.4% a week earlier. FEMA's flood data list 382 flood losses here since 2016, 38% of them in buildings with basements. 41% of homes were built before 1980, against 50% nationally; the median home dates from 1987.
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 Jefferson County
| Expansive clay (limits slab homes) | 37.0% |
| High water table (limits basements) | 34.0% |
| Septic fields very limited | 92.2% |
| Clay swell (LEP, by area) | 5.2% |
| High-swell land (LEP 6%+) | 38.6% |
| Urban land, not rated | 1.3% |
| Mapped soil | 425,280 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Sonsac | 18% | n/a |
| Useful | 13% | n/a |
| Wrengart | 6% | n/a |
| Caneyville | 6% | n/a |
| Rueter | 4% | n/a |
| Moko | 4% | n/a |
How we count · survey areas MO099 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 5.2% by land area here, and 39% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 37% of the mapped land.
Clay shrinks as it dries: 34.6% of the county is in drought on the latest map, and 37% of Jefferson County's mapped land has shrink-swell clay.
On 34% of Jefferson 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: 39.10 in, 4.74 in below the 1991-2020 average year of 43.84 in.
USDA rates 92% of the land very limited for septic absorption fields.
Drought
34.6% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 20 of the last 52 weeks; the most was 100% of its area, in 6 weeks, most recently on the February 10, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 34.6% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
382 flood losses since 2016, $12.8 million paid. The worst year was 2017, with 196. Foundations of the buildings, where recorded: 38% basements, 29% slabs, 10% crawl spaces, 24% elevated. Median water depth outside the building: 32 in.
| Year | Flood losses |
|---|---|
| 2016 | 41 |
| 2017 | 196 |
| 2018 | 8 |
| 2019 | 31 |
| 2020 | 9 |
| 2021 | 6 |
| 2022 | 28 |
| 2023 | 3 |
| 2024 | 56 |
| 2025 | 3 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 43.84 in |
| 12 months to August 2026 | 39.10 in (-4.74) |
| 2025 | 37.78 in (-6.06) |
| Wettest year since 1895 | 1957: 60.33 in |
| Driest year since 1895 | 1976: 24.58 in |
| Days with 1 inch or more, normal at FESTUS (8 mi away) | 12.3 |
Homes
| Housing units | 93,955 |
| Median year built | 1987 |
| Built before 1980 | 41% |
| Built 2000 or later | 29% |
| Owner-occupied | 82% |
| Median value, owner-occupied | $237,200 |
| Single-family detached | 80% |
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 |
|---|---|---|---|
| Monroe County, IL | 20 mi | 20% | 59% |
| St. Louis County, MO | 27 mi | 5% | 37% |
| Washington County, MO | 29 mi | 27% | 25% |
| Franklin County, MO | 31 mi | 14% | 61% |
| St. Louis city, MO | 31 mi | 1% | 32% |
| St. Francois County, MO | 31 mi | 15% | 40% |
| Ste. Genevieve County, MO | 33 mi | 16% | 34% |
| St. Clair County, IL | 36 mi | 28% | 73% |
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