Washtenaw County, Michigan
A shallow water table limits basements on 54% of Washtenaw County's mapped land, a higher share than 70% of US counties. Shrink-swell clay limits houses without basements on 7%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 30 flood losses here since 2016, 63% of them in buildings with basements. 53% of homes were built before 1980, against 50% nationally; the median home dates from 1978.
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 Washtenaw County
| Expansive clay (limits slab homes) | 7.4% |
| High water table (limits basements) | 53.8% |
| Septic fields very limited | 86.3% |
| Clay swell (LEP, by area) | 3.4% |
| High-swell land (LEP 6%+) | 6.0% |
| Mapped soil | 462,560 acres |
How we count · survey areas MI161 (2025-09-04)
What the numbers mean here
On 54% of Washtenaw 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: 29.34 in, 4.36 in below the 1991-2020 average year of 33.70 in.
USDA rates 86% 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 19 of the last 52 weeks; the most was 81.7% of its area, in 2 weeks, most recently on the January 6, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 49.5% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
30 flood losses since 2016, $811,002 paid. The worst year was 2024, with 6. Foundations of the buildings, where recorded: 63% basements, 13% slabs, 13% crawl spaces, 13% elevated.
| Year | Flood losses |
|---|---|
| 2016 | 3 |
| 2017 | 1 |
| 2018 | 1 |
| 2019 | 4 |
| 2020 | 1 |
| 2021 | 6 |
| 2022 | 2 |
| 2023 | 5 |
| 2024 | 6 |
| 2025 | 0 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 33.70 in |
| 12 months to August 2026 | 29.34 in (-4.36) |
| 2025 | 30.38 in (-3.32) |
| Wettest year since 1895 | 2011: 48.70 in |
| Driest year since 1895 | 1963: 18.45 in |
| Days with 1 inch or more, normal at ANN ARBOR U OF MICH (10 mi away) | 6.4 |
Homes
| Housing units | 159,782 |
| Median year built | 1978 |
| Built before 1980 | 53% |
| Built 2000 or later | 22% |
| Owner-occupied | 62% |
| Median value, owner-occupied | $374,100 |
| Single-family detached | 57% |
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 |
|---|---|---|---|
| Livingston County, MI | 24 mi | under 1% | 37% |
| Lenawee County, MI | 27 mi | 9% | 79% |
| Jackson County, MI | 30 mi | 0% | 38% |
| Monroe County, MI | 30 mi | 11% | 91% |
| Wayne County, MI | 30 mi | 6% | 66% |
| Ingham County, MI | 36 mi | 0% | 68% |
| Oakland County, MI | 37 mi | 1% | 34% |
| Lucas County, OH | 44 mi | 19% | 68% |
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