Washington County, Oregon
A shallow water table limits basements on 42% of Washington County's mapped land, a higher share than 60% of US counties and the highest of 35 Oregon 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 21 flood losses here since 2016. 36% of homes were built before 1980, against 50% nationally; the median home dates from 1990.
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) | 6.8% |
| High water table (limits basements) | 42.4% |
| Septic fields very limited | 96.6% |
| Clay swell (LEP, by area) | 3.5% |
| High-swell land (LEP 6%+) | 7.0% |
| Mapped soil | 465,485 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Olyic | 8% | n/a |
| Laurelwood | 8% | n/a |
| Melby | 8% | n/a |
| Woodburn | 8% | n/a |
| Aloha | 6% | n/a |
| Cornelius | 4% | n/a |
How we count · survey areas OR067 (2025-09-09)
What the numbers mean here
On 42% 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: 51.23 in, 4.49 in below the 1991-2020 average year of 55.72 in.
USDA rates 97% 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 8 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the December 2, 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
21 flood losses since 2016, $138,034 paid. The worst year was 2017, with 6.
| Year | Flood losses |
|---|---|
| 2016 | 2 |
| 2017 | 6 |
| 2018 | 1 |
| 2019 | 3 |
| 2020 | 1 |
| 2021 | 2 |
| 2022 | 3 |
| 2023 | 1 |
| 2024 | 0 |
| 2025 | 1 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 55.72 in |
| 12 months to August 2026 | 51.23 in (-4.49) |
| 2025 | 48.47 in (-7.25) |
| Wettest year since 1895 | 1996: 89.01 in |
| Driest year since 1895 | 1929: 33.21 in |
| Days with 1 inch or more, normal at DILLEY 2 S (6 mi away) | 7.1 |
Homes
| Housing units | 243,278 |
| Median year built | 1990 |
| Built before 1980 | 36% |
| Built 2000 or later | 31% |
| Owner-occupied | 61% |
| Median value, owner-occupied | $588,000 |
| 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 |
|---|---|---|---|
| Yamhill County, OR | 24 mi | 31% | 36% |
| Columbia County, OR | 27 mi | 7% | 35% |
| Tillamook County, OR | 33 mi | 1% | 5% |
| Multnomah County, OR | 33 mi | 0% | 30% |
| Clark County, WA | 33 mi | 3% | 22% |
| Clatsop County, OR | 44 mi | 1% | 12% |
| Polk County, OR | 47 mi | 18% | 30% |
| Cowlitz County, WA | 49 mi | 4% | 10% |
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