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Sanborn County, South Dakota
A shallow water table limits basements on 40% of Sanborn County's mapped land, a higher share than 58% of US counties. Shrink-swell clay limits houses without basements on 28%.
1.3% 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. 74% of homes were built before 1980, against 50% nationally; the median home dates from 1958.
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 Sanborn County
| Expansive clay (limits slab homes) | 27.8% |
| High water table (limits basements) | 40.3% |
| Septic fields very limited | 92.6% |
| Clay swell (LEP, by area) | 4.5% |
| High-swell land (LEP 6%+) | 28.4% |
| Mapped soil | 364,742 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Clarno | 18% | 0% |
| Tetonka | 10% | n/a |
| Houdek | 7% | n/a |
| Bonilla | 7% | n/a |
| Ethan | 7% | n/a |
| Carthage | 5% | n/a |
How we count · survey areas SD111 (2025-09-10)
What the numbers mean here
Clay swell averages a linear extensibility of 4.5% 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 28% of the mapped land.
Clay shrinks as it dries: 1.3% of the county is in drought on the latest map, and 28% of Sanborn County's mapped land has shrink-swell clay.
On 40% of Sanborn 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: 17.14 in, 7.06 in below the 1991-2020 average year of 24.20 in.
USDA rates 93% of the land very limited for septic absorption fields.
Drought
1.3% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 34 of the last 52 weeks; the most was 100% of its area, in 20 weeks, most recently on the July 28, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 64% |
| D1 moderate drought or worse | 1.3% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Sanborn County since 2016.
Rain
| Average year, 1991-2020 | 24.20 in |
| 12 months to August 2026 | 17.14 in (-7.06) |
| 2025 | 22.80 in (-1.40) |
| Wettest year since 1895 | 2019: 39.64 in |
| Driest year since 1895 | 1925: 11.90 in |
| Days with 1 inch or more, normal at FORESTBURG 4 NNE (3 mi away) | 5.6 |
Homes
| Housing units | 1,168 |
| Median year built | 1958 |
| Built before 1980 | 74% |
| Built 2000 or later | 12% |
| Owner-occupied | 79% |
| Median value, owner-occupied | $135,600 |
| Single-family detached | 80% |
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 |
|---|---|---|---|
| Davison County, SD | 24 mi | 18% | 20% |
| Miner County, SD | 24 mi | 41% | 28% |
| Jerauld County, SD | 27 mi | 34% | 22% |
| Hanson County, SD | 28 mi | 21% | 25% |
| Beadle County, SD | 29 mi | 37% | 30% |
| Aurora County, SD | 32 mi | 42% | 19% |
| Kingsbury County, SD | 38 mi | 30% | 50% |
| McCook County, SD | 43 mi | 26% | 33% |
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