HomeMissouriSt. Charles County
St. Charles County, Missouri
A shallow water table limits basements on 62% of St. Charles County's mapped land, a higher share than 75% of US counties. Shrink-swell clay limits houses without basements on 41%.
16.3% of the county is in drought on the October 13, 2026 Drought Monitor map, up from 11.3% a week earlier. FEMA's flood data list 823 flood losses here since 2016, 33% of them in buildings with basements. 25% of homes were built before 1980, against 50% nationally; the median home dates from 1994.
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. Charles County
| Expansive clay (limits slab homes) | 40.7% |
| High water table (limits basements) | 62.0% |
| Septic fields very limited | 84.8% |
| Clay swell (LEP, by area) | 6.1% |
| High-swell land (LEP 6%+) | 40.9% |
| Urban land, not rated | 5.7% |
| Mapped soil | 380,020 acres |
How we count · survey areas MO183 (2025-09-02)
What the numbers mean here
Clay swell averages a linear extensibility of 6.1% by land area here, and 41% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 41% of the mapped land.
Clay shrinks as it dries: 16.3% of the county is in drought on the latest map, and 41% of St. Charles County's mapped land has shrink-swell clay.
On 62% of St. Charles 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: 37.95 in, 4.34 in below the 1991-2020 average year of 42.29 in.
USDA rates 85% of the land very limited for septic absorption fields.
Drought
16.3% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 21 of the last 52 weeks; the most was 100% of its area, in 9 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 | 16.3% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
823 flood losses since 2016, $30.7 million paid. The worst year was 2019, with 474. Foundations of the buildings, where recorded: 33% basements, 16% slabs, 3% crawl spaces, 47% elevated. Median water depth outside the building: 33 in.
| Year | Flood losses |
|---|---|
| 2016 | 28 |
| 2017 | 60 |
| 2018 | 28 |
| 2019 | 474 |
| 2020 | 58 |
| 2021 | 13 |
| 2022 | 139 |
| 2023 | 2 |
| 2024 | 13 |
| 2025 | 2 |
| 2026 to date | 6 |
Rain
| Average year, 1991-2020 | 42.29 in |
| 12 months to August 2026 | 37.95 in (-4.34) |
| 2025 | 37.77 in (-4.52) |
| Wettest year since 1895 | 2008: 58.04 in |
| Driest year since 1895 | 1930: 24.09 in |
| Days with 1 inch or more, normal at WELDON SPRING NWS (6 mi away) | 12.2 |
Homes
| Housing units | 167,163 |
| Median year built | 1994 |
| Built before 1980 | 25% |
| Built 2000 or later | 39% |
| Owner-occupied | 81% |
| Median value, owner-occupied | $320,800 |
| Single-family detached | 75% |
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 |
|---|---|---|---|
| St. Louis County, MO | 16 mi | 5% | 37% |
| Lincoln County, MO | 25 mi | 64% | 55% |
| St. Louis city, MO | 25 mi | 1% | 32% |
| Warren County, MO | 26 mi | 52% | 59% |
| Calhoun County, IL | 26 mi | 4% | 25% |
| Jersey County, IL | 27 mi | 22% | 53% |
| Franklin County, MO | 33 mi | 14% | 61% |
| Jefferson County, MO | 37 mi | 37% | 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