Washington County, Iowa
A shallow water table limits basements on 88% of Washington County's mapped land, a higher share than 95% of US counties and the 7th highest of 99 Iowa counties. Shrink-swell clay limits houses without basements on 65%.
None 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. 66% of homes were built before 1980, against 50% nationally; the median home dates from 1964.
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 Washington County
| Expansive clay (limits slab homes) | 64.5% |
| High water table (limits basements) | 88.3% |
| Septic fields very limited | 99.1% |
| Clay swell (LEP, by area) | 6.1% |
| High-swell land (LEP 6%+) | 62.0% |
| Mapped soil | 365,200 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Clinton | 14% | n/a |
| Otley | 9% | n/a |
| Mahaska | 9% | n/a |
| Ladoga | 8% | n/a |
| Taintor | 6% | n/a |
| Nira | 6% | n/a |
How we count · survey areas IA183 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 6.1% by land area here, and 62% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 65% of the mapped land.
On 88% of Washington 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: 32.22 in, 5.82 in below the 1991-2020 average year of 38.04 in.
USDA rates 99% 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 18 of the last 52 weeks; the most was 100% of its area, in 16 weeks, most recently on the March 31, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 0% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Washington County since 2016.
Rain
| Average year, 1991-2020 | 38.04 in |
| 12 months to August 2026 | 32.22 in (-5.82) |
| 2025 | 31.36 in (-6.68) |
| Wettest year since 1895 | 2010: 55.06 in |
| Driest year since 1895 | 1988: 18.84 in |
| Days with 1 inch or more, normal at WASHINGTON (3 mi away) | 9.8 |
Homes
| Housing units | 9,657 |
| Median year built | 1964 |
| Built before 1980 | 66% |
| Built 2000 or later | 19% |
| Owner-occupied | 74% |
| Median value, owner-occupied | $203,900 |
| Single-family detached | 78% |
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 |
|---|---|---|---|
| Keokuk County, IA | 23 mi | 71% | 87% |
| Johnson County, IA | 25 mi | 40% | 56% |
| Louisa County, IA | 25 mi | 38% | 70% |
| Henry County, IA | 26 mi | 76% | 86% |
| Jefferson County, IA | 26 mi | 71% | 87% |
| Iowa County, IA | 30 mi | 57% | 69% |
| Muscatine County, IA | 33 mi | 20% | 50% |
| Des Moines County, IA | 40 mi | 57% | 80% |
Sources: USDA SSURGO (September 9, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status