HomeSouth DakotaBon Homme County

Bon Homme County, South Dakota

Shrink-swell clay limits houses without basements on 27% of Bon Homme County's mapped land, a higher share than 77% of US counties. A shallow water table limits basements on 26%.

33.5% 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. 75% of homes were built before 1980, against 50% nationally; the median home dates from 1958.

Data as of October 13, 2026 · sources

27%

expansive clay: shrink-swell limits slab homes

26%

high water table: limits basements

34%

in drought, October 13, 2026

75%

of homes built before 1980

Soil under Bon Homme County

Expansive clay (limits slab homes)26.7%
High water table (limits basements)26.5%
Septic fields very limited88.4%
Clay swell (LEP, by area)4.7%
High-swell land (LEP 6%+)27.0%
Mapped soil373,734 acres
Soil seriesShare hereSeries nationally: expansive clay
Clarno18%0%
Homme15%n/a
Ethan13%n/a
Tetonka6%n/a
Bonilla6%n/a
Crossplain6%n/a
Knox County: 16%Yankton County: 21%Hutchinson County: 21%Douglas County: 33%Charles Mix County: 29%Cedar County: 2%Turner County: 20%Boyd County: 52%Bon Homme County KnoxYanktonHutchinsonDouglasCharles MixCedarTurnerBoydBon Homme
Bon Homme 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 SD009 (2025-09-09)

What the numbers mean here

Clay swell averages a linear extensibility of 4.7% 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 27% of the mapped land.

Clay shrinks as it dries: 33.5% of the county is in drought on the latest map, and 27% of Bon Homme County's mapped land has shrink-swell clay.

On 26% of Bon Homme 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: 14.67 in, 11.93 in below the 1991-2020 average year of 26.60 in.

USDA rates 88% of the land very limited for septic absorption fields.

Drought

33.5% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 52 of the last 52 weeks; the most was 100% of its area, in 45 weeks, most recently on the September 8, 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 worse33.5%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

2 flood losses since 2016, $24,184 paid. The worst year was 2019, with 2.

YearFlood losses
20160
20170
20180
20192
20200
20210
20220
20230
20240
20250
2026 to date0

Rain

Average year, 1991-202026.60 in
12 months to August 202614.67 in (-11.93)
202528.29 in (+1.69)
Wettest year since 18951944: 38.40 in
Driest year since 18951974: 14.02 in
Days with 1 inch or more, normal at TYNDALL (1 mi away)5.8

Homes

Housing units2,842
Median year built1958
Built before 198075%
Built 2000 or later12%
Owner-occupied81%
Median value, owner-occupied$134,100
Single-family detached86%

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
Knox County, NE 24 mi 16% 6%
Yankton County, SD 25 mi 21% 30%
Hutchinson County, SD 25 mi 21% 25%
Douglas County, SD 37 mi 33% 21%
Charles Mix County, SD 39 mi 29% 13%
Cedar County, NE 41 mi 2% 7%
Turner County, SD 43 mi 20% 39%
Boyd County, NE 45 mi 52% 13%

Sources: USDA SSURGO (September 9, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status