HomeSouth DakotaDewey County

Dewey County, South Dakota

Shrink-swell clay limits houses without basements on 70% of Dewey County's mapped land, a higher share than 97% of US counties and the 6th highest of 66 South Dakota counties. A shallow water table limits basements on 4%.

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. 55% of homes were built before 1980, against 50% nationally; the median home dates from 1978.

Data as of October 13, 2026 · sources

70%

expansive clay: shrink-swell limits slab homes

4%

high water table: limits basements

100%

in drought, October 13, 2026

55%

of homes built before 1980

Soil under Dewey County

Expansive clay (limits slab homes)70.0%
High water table (limits basements)3.8%
Septic fields very limited88.9%
Clay swell (LEP, by area)10.2%
High-swell land (LEP 6%+)72.8%
Mapped soil1,565,587 acres
Soil seriesShare hereSeries nationally: expansive clay
Opal18%n/a
Sansarc17%n/a
Dupree6%n/a
Promise5%n/a
Morton4%n/a
Vebar4%n/a
Corson County: 34%Ziebach County: 59%Potter County: 25%Walworth County: 26%Sully County: 23%Stanley County: 89%Campbell County: 18%Sioux County: 33%Dewey County CorsonZiebachPotterWalworthSullyStanleyCampbellSiouxDewey
Dewey 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 SD041 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 10.2% by land area here, and 73% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 70% of the mapped land.

Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 70% of Dewey County's mapped land has shrink-swell clay.

Rain over the 12 months to August 2026: 18.10 in, 0.59 in below the 1991-2020 average year of 18.69 in.

USDA rates 89% 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 16 of the last 52 weeks; the most was 100% of its area, in 12 weeks, most recently on the October 13, 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 worse100%
D2 severe or worse52.9%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

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

Rain

Average year, 1991-202018.69 in
12 months to August 202618.10 in (-0.59)
202525.88 in (+7.19)
Wettest year since 18952019: 29.16 in
Driest year since 18951936: 7.68 in
Days with 1 inch or more, normal at TIMBER LAKE (23 mi away)3.4

Homes

Housing units1,931
Median year built1978
Built before 198055%
Built 2000 or later16%
Owner-occupied61%
Median value, owner-occupied$69,600
Single-family detached76%

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
Corson County, SD 41 mi 34% 3%
Ziebach County, SD 42 mi 59% 2%
Potter County, SD 43 mi 25% 11%
Walworth County, SD 44 mi 26% 10%
Sully County, SD 45 mi 23% 9%
Stanley County, SD 51 mi 89% 6%
Campbell County, SD 60 mi 18% 13%
Sioux County, ND 67 mi 33% 3%

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