HomeSouth DakotaMellette County

Mellette County, South Dakota

Shrink-swell clay limits houses without basements on 61% of Mellette County's mapped land, a higher share than 94% of US counties and the 9th highest of 66 South Dakota counties. A shallow water table limits basements on 3%.

None 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. 71% 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

3%

high water table: limits basements

0%

in drought, October 13, 2026

71%

of homes built before 1980

Soil under Mellette County

Expansive clay (limits slab homes)60.6%
High water table (limits basements)2.8%
Septic fields very limited88.3%
Clay swell (LEP, by area)8.4%
High-swell land (LEP 6%+)69.3%
Mapped soil838,912 acres
Soil seriesShare hereSeries nationally: expansive clay
Lakoma10%n/a
Okaton9%n/a
Promise6%n/a
Imlay6%n/a
Norrest5%n/a
Opal5%n/a
Todd County: 12%Jones County: 94%Jackson County: 45%Tripp County: 61%Lyman County: 89%Bennett County: 10%Stanley County: 89%Haakon County: 89%Mellette County ToddJonesJacksonTrippLymanBennettStanleyHaakonMellette
Mellette 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 SD095 (2025-09-10)

What the numbers mean here

Clay swell averages a linear extensibility of 8.4% by land area here, and 69% 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.

Rain over the 12 months to August 2026: 19.64 in, 1.12 in below the 1991-2020 average year of 20.76 in.

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

Drought

0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 36 of the last 52 weeks; the most was 100% of its area, in 15 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 worse86.3%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

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

Rain

Average year, 1991-202020.76 in
12 months to August 202619.64 in (-1.12)
202520.87 in (+0.11)
Wettest year since 18952019: 30.81 in
Driest year since 18951974: 10.71 in
Days with 1 inch or more, normal at WOOD (15 mi away)3.9

Homes

Housing units779
Median year built1969
Built before 198071%
Built 2000 or later11%
Owner-occupied60%
Median value, owner-occupied$84,100
Single-family detached74%

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
Todd County, SD 26 mi 12% 9%
Jones County, SD 26 mi 94% 7%
Jackson County, SD 44 mi 45% 2%
Tripp County, SD 47 mi 61% 9%
Lyman County, SD 50 mi 89% 8%
Bennett County, SD 54 mi 10% 8%
Stanley County, SD 58 mi 89% 6%
Haakon County, SD 63 mi 89% 6%

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