St. Clair County, Michigan
A shallow water table limits basements on 90% of St. Clair County's mapped land, a higher share than 96% of US counties and the 7th highest of 83 Michigan counties. Shrink-swell clay limits houses without basements on 23%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 284 flood losses here since 2016, 10% of them in buildings with basements. 57% of homes were built before 1980, against 50% nationally; the median home dates from 1975.
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) | 22.8% |
| High water table (limits basements) | 90.1% |
| Septic fields very limited | 95.9% |
| Clay swell (LEP, by area) | 4.0% |
| High-swell land (LEP 6%+) | 24.1% |
| Mapped soil | 481,005 acres |
How we count · survey areas MI147 (2025-09-04)
What the numbers mean here
Clay swell averages a linear extensibility of 4.0% by land area here, and 24% 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.
On 90% 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: 31.72 in, 2.17 in below the 1991-2020 average year of 33.89 in.
USDA rates 96% of the land very limited for septic absorption fields.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 14 of the last 52 weeks; the most was 100% of its area, on the October 21, 2025 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
284 flood losses since 2016, $2.3 million paid. The worst year was 2019, with 143. Foundations of the buildings, where recorded: 10% basements, 16% slabs, 64% crawl spaces, 10% elevated. Median water depth outside the building: 7 in.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 0 |
| 2018 | 19 |
| 2019 | 143 |
| 2020 | 59 |
| 2021 | 44 |
| 2022 | 1 |
| 2023 | 7 |
| 2024 | 6 |
| 2025 | 1 |
| 2026 to date | 3 |
Rain
| Average year, 1991-2020 | 33.89 in |
| 12 months to August 2026 | 31.72 in (-2.17) |
| 2025 | 30.43 in (-3.46) |
| Wettest year since 1895 | 2011: 43.09 in |
| Driest year since 1895 | 1963: 17.69 in |
| Days with 1 inch or more, normal at PORT HURON (13 mi away) | 5.7 |
Homes
| Housing units | 72,799 |
| Median year built | 1975 |
| Built before 1980 | 57% |
| Built 2000 or later | 17% |
| Owner-occupied | 81% |
| Median value, owner-occupied | $224,600 |
| Single-family detached | 79% |
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 |
|---|---|---|---|
| Macomb County, MI | 22 mi | 9% | 80% |
| Lapeer County, MI | 30 mi | 4% | 60% |
| Sanilac County, MI | 36 mi | 1% | 78% |
| Oakland County, MI | 41 mi | 1% | 34% |
| Genesee County, MI | 53 mi | under 1% | 72% |
| Wayne County, MI | 54 mi | 6% | 66% |
| Tuscola County, MI | 55 mi | under 1% | 84% |
| Livingston County, MI | 67 mi | under 1% | 37% |
Sources: USDA SSURGO (September 4, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status