Yamhill County, Oregon
A shallow water table limits basements on 36% of Yamhill County's mapped land, a higher share than 55% of US counties and the 3rd highest of 35 Oregon counties. Shrink-swell clay limits houses without basements on 31%.
15.2% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 6 flood losses here since 2016. 38% 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 Yamhill County
| Expansive clay (limits slab homes) | 31.5% |
| High water table (limits basements) | 36.3% |
| Septic fields very limited | 97.1% |
| Clay swell (LEP, by area) | 5.1% |
| High-swell land (LEP 6%+) | 30.0% |
| Mapped soil | 459,840 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Woodburn | 11% | n/a |
| Jory | 6% | n/a |
| Saum | 5% | n/a |
| Olyic | 5% | n/a |
| Amity | 5% | n/a |
| Melbourne | 5% | n/a |
How we count · survey areas OR071 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 5.1% by land area here, and 30% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 31% of the mapped land.
Clay shrinks as it dries: 15.2% of the county is in drought on the latest map, and 31% of Yamhill County's mapped land has shrink-swell clay.
On 36% of Yamhill 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: 54.38 in, 5.70 in below the 1991-2020 average year of 60.08 in.
USDA rates 97% of the land very limited for septic absorption fields.
Drought
15.2% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 31 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 | 15.2% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
6 flood losses since 2016, $29,086 paid. The worst year was 2017, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 4 |
| 2018 | 0 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 2 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 60.08 in |
| 12 months to August 2026 | 54.38 in (-5.70) |
| 2025 | 52.65 in (-7.43) |
| Wettest year since 1895 | 1996: 97.23 in |
| Driest year since 1895 | 1929: 36.40 in |
| Days with 1 inch or more, normal at HASKINS DAM (5 mi away) | 21.7 |
Homes
| Housing units | 41,200 |
| Median year built | 1990 |
| Built before 1980 | 38% |
| Built 2000 or later | 31% |
| Owner-occupied | 69% |
| Median value, owner-occupied | $471,700 |
| Single-family detached | 68% |
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 |
|---|---|---|---|
| Washington County, OR | 24 mi | 7% | 42% |
| Polk County, OR | 24 mi | 18% | 30% |
| Tillamook County, OR | 26 mi | 1% | 5% |
| Marion County, OR | 43 mi | 19% | 40% |
| Multnomah County, OR | 48 mi | 0% | 30% |
| Columbia County, OR | 49 mi | 7% | 35% |
| Benton County, OR | 51 mi | 22% | 24% |
| Lincoln County, OR | 51 mi | 1% | 6% |
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