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Day County, South Dakota

A shallow water table limits basements on 63% of Day County's mapped land, a higher share than 77% of US counties and the 6th highest of 66 South Dakota counties. Shrink-swell clay limits houses without basements on 19%.

27.4% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 5 flood losses here since 2016. 67% of homes were built before 1980, against 50% nationally; the median home dates from 1967.

Data as of October 13, 2026 · sources

19%

expansive clay: shrink-swell limits slab homes

63%

high water table: limits basements

27%

in drought, October 13, 2026

67%

of homes built before 1980

Soil under Day County

Expansive clay (limits slab homes)18.8%
High water table (limits basements)63.4%
Septic fields very limited94.3%
Clay swell (LEP, by area)4.5%
High-swell land (LEP 6%+)18.8%
Mapped soil698,195 acres
Soil seriesShare hereSeries nationally: high water table
Buse16%n/a
Forman15%n/a
Aastad8%n/a
Southam6%n/a
Kranzburg6%n/a
Parnell4%n/a
Marshall County: 57%Codington County: 65%Clark County: 65%Roberts County: 60%Brown County: 56%Grant County: 56%Spink County: 56%Hamlin County: 67%Day County MarshallCodingtonClarkRobertsBrownGrantSpinkHamlinDay
Day 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 SD037 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 4.5% by land area here, and 19% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 19% of the mapped land.

Clay shrinks as it dries: 27.4% of the county is in drought on the latest map, and 19% of Day County's mapped land has shrink-swell clay.

On 63% of Day 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: 20.73 in, 2.99 in below the 1991-2020 average year of 23.72 in.

USDA rates 94% of the land very limited for septic absorption fields.

Drought

27.4% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 5 of the last 52 weeks; the most was 27.4% of its area, in 3 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 worse75.5%
D1 moderate drought or worse27.4%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

5 flood losses since 2016, $143,949 paid. The worst year was 2020, with 4.

YearFlood losses
20160
20170
20180
20190
20204
20210
20220
20230
20240
20250
2026 to date1

Rain

Average year, 1991-202023.72 in
12 months to August 202620.73 in (-2.99)
202526.89 in (+3.17)
Wettest year since 18952019: 34.01 in
Driest year since 18951976: 8.21 in
Days with 1 inch or more, normal at WEBSTER (3 mi away)5.6

Homes

Housing units3,440
Median year built1967
Built before 198067%
Built 2000 or later19%
Owner-occupied75%
Median value, owner-occupied$173,600
Single-family detached85%

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
Marshall County, SD 26 mi 22% 57%
Codington County, SD 33 mi 11% 65%
Clark County, SD 35 mi 19% 65%
Roberts County, SD 36 mi 26% 60%
Brown County, SD 41 mi 28% 56%
Grant County, SD 41 mi 26% 56%
Spink County, SD 47 mi 45% 56%
Hamlin County, SD 51 mi 13% 67%

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