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Walworth County, South Dakota
Shrink-swell clay limits houses without basements on 26% of Walworth County's mapped land, a higher share than 76% of US counties. A shallow water table limits basements on 10%.
60.7% 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. 69% of homes were built before 1980, against 50% nationally; the median home dates from 1969.
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 Walworth County
| Expansive clay (limits slab homes) | 25.8% |
| High water table (limits basements) | 9.6% |
| Septic fields very limited | 42.3% |
| Clay swell (LEP, by area) | 6.0% |
| High-swell land (LEP 6%+) | 28.0% |
| Mapped soil | 472,966 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Highmore | 26% | n/a |
| Mobridge | 7% | n/a |
| Williams | 5% | 0% |
| Opal | 5% | n/a |
| Agar | 4% | n/a |
| Bearpaw | 3% | n/a |
How we count · survey areas SD129 (2025-09-10)
What the numbers mean here
Clay swell averages a linear extensibility of 6.0% by land area here, and 28% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 26% of the mapped land.
Clay shrinks as it dries: 60.7% of the county is in drought on the latest map, and 26% of Walworth County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 19.55 in, 0.07 in below the 1991-2020 average year of 19.62 in.
Drought
60.7% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 15 of the last 52 weeks; the most was 70.4% of its area, in 9 weeks, most recently on the September 29, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 60.7% |
| D2 severe or worse | 25.1% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Walworth County since 2016.
Rain
| Average year, 1991-2020 | 19.62 in |
| 12 months to August 2026 | 19.55 in (-0.07) |
| 2025 | 25.25 in (+5.63) |
| Wettest year since 1895 | 1915: 28.95 in |
| Driest year since 1895 | 1934: 7.54 in |
| Days with 1 inch or more, normal at SELBY (6 mi away) | 3.4 |
Homes
| Housing units | 2,932 |
| Median year built | 1969 |
| Built before 1980 | 69% |
| Built 2000 or later | 16% |
| Owner-occupied | 76% |
| Median value, owner-occupied | $136,600 |
| Single-family detached | 79% |
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 |
|---|---|---|---|
| Campbell County, SD | 25 mi | 18% | 13% |
| Potter County, SD | 26 mi | 25% | 11% |
| Edmunds County, SD | 40 mi | 22% | 25% |
| Dewey County, SD | 44 mi | 70% | 4% |
| McPherson County, SD | 48 mi | 18% | 22% |
| Sully County, SD | 49 mi | 23% | 9% |
| Faulk County, SD | 49 mi | 20% | 23% |
| McIntosh County, ND | 54 mi | 22% | 12% |
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