Benton County, Oregon
A shallow water table limits basements on 24% of Benton County's mapped land and the 9th highest of 35 Oregon counties. Shrink-swell clay limits houses without basements on 22%.
98.6% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 7 flood losses here since 2016. 52% of homes were built before 1980, against 50% nationally; the median home dates from 1979.
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 Benton County
| Expansive clay (limits slab homes) | 21.8% |
| High water table (limits basements) | 24.1% |
| Septic fields very limited | 92.4% |
| Clay swell (LEP, by area) | 4.8% |
| High-swell land (LEP 6%+) | 19.8% |
| Mapped soil | 434,521 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Jory | 11% | n/a |
| Honeygrove | 5% | n/a |
| Bohannon | 4% | n/a |
| Preacher | 4% | n/a |
| Dayton | 3% | n/a |
| Bellpine | 3% | n/a |
How we count · survey areas OR003 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 4.8% by land area here, and 20% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 22% of the mapped land.
Clay shrinks as it dries: 98.6% of the county is in drought on the latest map, and 22% of Benton County's mapped land has shrink-swell clay.
On 24% of Benton 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: 42.16 in, 17.27 in below the 1991-2020 average year of 59.43 in.
USDA rates 92% of the land very limited for septic absorption fields.
Drought
98.6% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 38 of the last 52 weeks; the most was 100% of its area, in 8 weeks, most recently on the September 15, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 98.6% |
| D2 severe or worse | 58.1% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
7 flood losses since 2016, $16,266 paid. The worst year was 2019, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 4 |
| 2020 | 0 |
| 2021 | 1 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 1 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 59.43 in |
| 12 months to August 2026 | 42.16 in (-17.27) |
| 2025 | 49.42 in (-10.01) |
| Wettest year since 1895 | 1996: 94.51 in |
| Driest year since 1895 | 2013: 35.15 in |
| Days with 1 inch or more, normal at CORVALLIS WATER BUREAU (2 mi away) | 19.7 |
Homes
| Housing units | 40,951 |
| Median year built | 1979 |
| Built before 1980 | 52% |
| Built 2000 or later | 25% |
| Owner-occupied | 57% |
| Median value, owner-occupied | $513,000 |
| Single-family detached | 59% |
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 |
|---|---|---|---|
| Lincoln County, OR | 26 mi | 1% | 6% |
| Polk County, OR | 27 mi | 18% | 30% |
| Linn County, OR | 43 mi | 25% | 34% |
| Lane County, OR | 48 mi | 12% | 14% |
| Marion County, OR | 49 mi | 19% | 40% |
| Yamhill County, OR | 51 mi | 31% | 36% |
| Tillamook County, OR | 67 mi | 1% | 5% |
| Washington County, OR | 74 mi | 7% | 42% |
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