Sioux County, Iowa
A shallow water table limits basements on 35% of Sioux County's mapped land, a higher share than 53% of US counties. Shrink-swell clay limits houses without basements on 26%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 32 flood losses here since 2016, 62% of them in buildings with basements. 63% of homes were built before 1980, against 50% nationally; the median home dates from 1973.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Sioux County
| Expansive clay (limits slab homes) | 25.9% |
| High water table (limits basements) | 34.9% |
| Septic fields very limited | 95.7% |
| Clay swell (LEP, by area) | 5.0% |
| High-swell land (LEP 6%+) | 16.1% |
| Mapped soil | 492,000 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Galva | 49% | n/a |
| Primghar | 14% | n/a |
| Colo | 4% | n/a |
| Radford | 4% | n/a |
| Moody | 4% | 0% |
| Marcus | 3% | n/a |
How we count · survey areas IA167 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 5.0% by land area here, and 16% 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.
On 35% of Sioux 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: 21.07 in, 8.29 in below the 1991-2020 average year of 29.36 in.
USDA rates 96% 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 47 of the last 52 weeks; the most was 100% of its area, in 11 weeks, most recently on the September 1, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 0% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
32 flood losses since 2016, $3.9 million paid. The worst year was 2024, with 25. Foundations of the buildings, where recorded: 62% basements, 23% slabs, 4% crawl spaces, 12% elevated. Median water depth outside the building: 49 in.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 0 |
| 2018 | 5 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 25 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 29.36 in |
| 12 months to August 2026 | 21.07 in (-8.29) |
| 2025 | 29.30 in (-0.06) |
| Wettest year since 1895 | 2018: 46.22 in |
| Driest year since 1895 | 1958: 14.57 in |
| Days with 1 inch or more, normal at SIOUX CTR 2 SE (2 mi away) | 6.2 |
Homes
| Housing units | 13,285 |
| Median year built | 1973 |
| Built before 1980 | 63% |
| Built 2000 or later | 22% |
| Owner-occupied | 76% |
| Median value, owner-occupied | $250,100 |
| Single-family detached | 80% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Lyon County, IA | 21 mi | 18% | 37% |
| Plymouth County, IA | 24 mi | 8% | 27% |
| O'Brien County, IA | 28 mi | 47% | 64% |
| Union County, SD | 30 mi | 33% | 42% |
| Lincoln County, SD | 31 mi | 28% | 51% |
| Osceola County, IA | 34 mi | 21% | 76% |
| Cherokee County, IA | 36 mi | 27% | 36% |
| Rock County, MN | 41 mi | 24% | 54% |
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