Jefferson County, Oregon
Shrink-swell clay limits houses without basements on 29% of Jefferson County's mapped land, a higher share than 79% of US counties and the 6th highest of 35 Oregon counties. A shallow water table limits basements on 1%.
100% 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. 35% of homes were built before 1980, against 50% nationally; the median home dates from 1991.
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 Jefferson County
| Expansive clay (limits slab homes) | 29.1% |
| High water table (limits basements) | 1.3% |
| Septic fields very limited | 95.3% |
| Clay swell (LEP, by area) | 4.5% |
| High-swell land (LEP 6%+) | 31.9% |
| Mapped soil | 1,113,777 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Tub | 10% | n/a |
| Madras | 8% | n/a |
| Simas | 7% | n/a |
| Curant | 4% | n/a |
| Lickskillet | 4% | n/a |
| Smiling | 3% | n/a |
How we count · survey areas OR620 (2025-09-10), OR666 (2025-09-10), OR674 (2025-09-10)
What the numbers mean here
Clay swell averages a linear extensibility of 4.5% by land area here, and 32% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 29% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 29% of Jefferson County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 15.77 in, 2.59 in below the 1991-2020 average year of 18.36 in.
USDA rates 95% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 42 of the last 52 weeks; the most was 100% of its area, in 32 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 100% |
| D3 extreme or worse | 89.9% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Jefferson County since 2016.
Rain
| Average year, 1991-2020 | 18.36 in |
| 12 months to August 2026 | 15.77 in (-2.59) |
| 2025 | 17.54 in (-0.82) |
| Wettest year since 1895 | 1996: 31.51 in |
| Driest year since 1895 | 1930: 11.53 in |
| Days with 1 inch or more, normal at PELTON DAM (7 mi away) | 0.3 |
Homes
| Housing units | 10,602 |
| Median year built | 1991 |
| Built before 1980 | 35% |
| Built 2000 or later | 30% |
| Owner-occupied | 72% |
| Median value, owner-occupied | $374,200 |
| Single-family detached | 73% |
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 |
|---|---|---|---|
| Wasco County, OR | 36 mi | 15% | 2% |
| Deschutes County, OR | 51 mi | 9% | 5% |
| Crook County, OR | 52 mi | n/a | n/a |
| Wheeler County, OR | 57 mi | 27% | 1% |
| Sherman County, OR | 58 mi | 0% | 1% |
| Clackamas County, OR | 61 mi | 5% | 30% |
| Hood River County, OR | 64 mi | 0% | 5% |
| Gilliam County, OR | 67 mi | 3% | under 1% |
Sources: USDA SSURGO (September 10, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status