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Tripp County, South Dakota

Shrink-swell clay limits houses without basements on 61% of Tripp County's mapped land, a higher share than 94% of US counties and the 8th highest of 66 South Dakota counties. A shallow water table limits basements on 9%.

56.4% 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. 68% of homes were built before 1980, against 50% nationally; the median home dates from 1969.

Data as of October 13, 2026 · sources

61%

expansive clay: shrink-swell limits slab homes

9%

high water table: limits basements

56%

in drought, October 13, 2026

68%

of homes built before 1980

Soil under Tripp County

Expansive clay (limits slab homes)60.8%
High water table (limits basements)8.8%
Septic fields very limited94.0%
Clay swell (LEP, by area)7.3%
High-swell land (LEP 6%+)57.6%
Mapped soil1,035,904 acres
Soil seriesShare hereSeries nationally: expansive clay
Millboro17%n/a
Anselmo7%n/a
Lakoma6%n/a
Reliance6%n/a
Doger6%n/a
Ree4%n/a
Keya Paha County: 8%Gregory County: 68%Lyman County: 89%Todd County: 12%Mellette County: 61%Brule County: 43%Jones County: 94%Buffalo County: 43%Tripp County Keya PahaGregoryLymanToddMelletteBruleJonesBuffaloTripp
Tripp 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 SD123 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 7.3% by land area here, and 58% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 61% of the mapped land.

Clay shrinks as it dries: 56.4% of the county is in drought on the latest map, and 61% of Tripp County's mapped land has shrink-swell clay.

Rain over the 12 months to August 2026: 19.47 in, 2.69 in below the 1991-2020 average year of 22.16 in.

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

Drought

56.4% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 39 of the last 52 weeks; the most was 100% of its area, in 25 weeks, most recently on the August 18, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse91.8%
D1 moderate drought or worse56.4%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

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

Rain

Average year, 1991-202022.16 in
12 months to August 202619.47 in (-2.69)
202521.97 in (-0.19)
Wettest year since 18951977: 33.78 in
Driest year since 18951934: 11.46 in
Days with 1 inch or more, normal at WINNER (2 mi away)4.7

Homes

Housing units2,762
Median year built1969
Built before 198068%
Built 2000 or later17%
Owner-occupied68%
Median value, owner-occupied$132,900
Single-family detached77%

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
Keya Paha County, NE 34 mi 8% 15%
Gregory County, SD 36 mi 68% 7%
Lyman County, SD 38 mi 89% 8%
Todd County, SD 43 mi 12% 9%
Mellette County, SD 47 mi 61% 3%
Brule County, SD 47 mi 43% 12%
Jones County, SD 58 mi 94% 7%
Buffalo County, SD 59 mi 43% 12%

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