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Grant County, South Dakota

A shallow water table limits basements on 56% of Grant County's mapped land, a higher share than 71% of US counties. Shrink-swell clay limits houses without basements on 26%.

52.5% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 2 flood losses here since 2016. 65% of homes were built before 1980, against 50% nationally; the median home dates from 1972.

Data as of October 13, 2026 · sources

26%

expansive clay: shrink-swell limits slab homes

56%

high water table: limits basements

53%

in drought, October 13, 2026

65%

of homes built before 1980

Soil under Grant County

Expansive clay (limits slab homes)26.1%
High water table (limits basements)55.6%
Septic fields very limited93.5%
Clay swell (LEP, by area)4.8%
High-swell land (LEP 6%+)26.7%
Mapped soil439,898 acres
Soil seriesShare hereSeries nationally: high water table
Peever14%n/a
Forman12%n/a
Buse7%n/a
LaDelle6%n/a
Aastad5%n/a
Vienna5%n/a
Big Stone County: 73%Codington County: 65%Deuel County: 71%Lac qui Parle County: 74%Roberts County: 60%Hamlin County: 67%Day County: 63%Traverse County: 94%Grant County Big StoneCodingtonDeuelLac qui ParleRobertsHamlinDayTraverseGrant
Grant County (heavy outline) and nearby counties, shaded by high water table share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas SD051 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 4.8% by land area here, and 27% 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: 52.5% of the county is in drought on the latest map, and 26% of Grant County's mapped land has shrink-swell clay.

On 56% of Grant 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: 18.57 in, 7.02 in below the 1991-2020 average year of 25.59 in.

USDA rates 93% of the land very limited for septic absorption fields.

Drought

52.5% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 17 of the last 52 weeks; the most was 74.5% of its area, in 2 weeks, most recently on the June 23, 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 worse52.5%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

2 flood losses since 2016, $15,878 paid. The worst year was 2026, with 1.

YearFlood losses
20160
20170
20180
20191
20200
20210
20220
20230
20240
20250
2026 to date1

Rain

Average year, 1991-202025.59 in
12 months to August 202618.57 in (-7.02)
202530.14 in (+4.55)
Wettest year since 18951977: 35.54 in
Driest year since 18951976: 9.15 in
Days with 1 inch or more, normal at BIG STONE CITY 2 NW (16 mi away)5.8

Homes

Housing units3,456
Median year built1972
Built before 198065%
Built 2000 or later16%
Owner-occupied76%
Median value, owner-occupied$171,000
Single-family detached76%

What repairs cost

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

WorkRangeSource
Basement waterproofing, US $3,000 to $10,000 Fixr, February 6, 2026
Sump pump installation, US $800 to $2,000 Fixr, January 31, 2025
Crawl space encapsulation, US $2,000 to $8,000 Fixr, August 29, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Big Stone County, MN 25 mi 15% 73%
Codington County, SD 25 mi 11% 65%
Deuel County, SD 29 mi 13% 71%
Lac qui Parle County, MN 31 mi 9% 74%
Roberts County, SD 32 mi 26% 60%
Hamlin County, SD 39 mi 13% 67%
Day County, SD 41 mi 19% 63%
Traverse County, MN 44 mi 21% 94%

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