HomeSouth DakotaCorson County

Corson County, South Dakota

Shrink-swell clay limits houses without basements on 34% of Corson County's mapped land, a higher share than 84% of US counties. A shallow water table limits basements on 3%.

89% 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. 60% of homes were built before 1980, against 50% nationally; the median home dates from 1974.

Data as of October 13, 2026 · sources

34%

expansive clay: shrink-swell limits slab homes

3%

high water table: limits basements

89%

in drought, October 13, 2026

60%

of homes built before 1980

Soil under Corson County

Expansive clay (limits slab homes)34.5%
High water table (limits basements)2.5%
Septic fields very limited81.5%
Clay swell (LEP, by area)5.4%
High-swell land (LEP 6%+)36.4%
Mapped soil1,620,794 acres
Soil seriesShare hereSeries nationally: expansive clay
Reeder12%n/a
Rhoades8%n/a
Cabba7%n/a
Vebar7%n/a
Daglum5%n/a
Bullock4%n/a
Sioux County: 33%Dewey County: 70%Grant County: 23%Ziebach County: 59%Campbell County: 18%Walworth County: 26%Emmons County: 14%Perkins County: 18%Corson County SiouxDeweyGrantZiebachCampbellWalworthEmmonsPerkinsCorson
Corson County (heavy outline) and nearby counties, shaded by expansive clay share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas SD031 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 5.4% by land area here, and 36% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 34% of the mapped land.

Clay shrinks as it dries: 89% of the county is in drought on the latest map, and 34% of Corson County's mapped land has shrink-swell clay.

Rain over the 12 months to August 2026: 18.04 in, 0.34 in below the 1991-2020 average year of 18.38 in.

USDA rates 82% of the land very limited for septic absorption fields.

Drought

89% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 16 of the last 52 weeks; the most was 100% of its area, in 9 weeks, most recently on the September 29, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse100%
D1 moderate drought or worse89%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

FEMA's flood data list no flood losses in Corson County since 2016.

Rain

Average year, 1991-202018.38 in
12 months to August 202618.04 in (-0.34)
202525.64 in (+7.26)
Wettest year since 18952019: 29.29 in
Driest year since 18951936: 6.27 in
Days with 1 inch or more, normal at MC INTOSH 6 SE (11 mi away)3

Homes

Housing units1,359
Median year built1974
Built before 198060%
Built 2000 or later22%
Owner-occupied59%
Median value, owner-occupied$69,800
Single-family detached84%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Foundation repair, US $2,200 to $8,200 Fixr, January 27, 2026
Pier-and-beam repair, US $2,000 to $15,000 Fixr, January 27, 2026
Foundation inspection, US $300 to $600 Fixr, January 31, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Sioux County, ND 30 mi 33% 3%
Dewey County, SD 41 mi 70% 4%
Grant County, ND 51 mi 23% 5%
Ziebach County, SD 54 mi 59% 2%
Campbell County, SD 57 mi 18% 13%
Walworth County, SD 59 mi 26% 10%
Emmons County, ND 61 mi 14% 7%
Perkins County, SD 64 mi 18% 2%

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