Shelby County, Iowa
Shrink-swell clay limits houses without basements on 21% of Shelby County's mapped land, a higher share than 71% of US counties. A shallow water table limits basements on 21%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 1 flood losses here since 2016. 79% of homes were built before 1980, against 50% nationally; the median home dates from 1949.
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 Shelby County
| Expansive clay (limits slab homes) | 20.7% |
| High water table (limits basements) | 20.5% |
| Septic fields very limited | 77.0% |
| Clay swell (LEP, by area) | 4.6% |
| High-swell land (LEP 6%+) | 3.5% |
| Mapped soil | 378,300 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Monona | 23% | n/a |
| Marshall | 15% | 14% |
| Exira | 15% | n/a |
| Judson | 14% | n/a |
| Ackmore | 9% | n/a |
| Ida | 6% | n/a |
How we count · survey areas IA165 (2025-09-09)
What the numbers mean here
Clay swell averages a linear extensibility of 4.6% by land area here, and 3% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 21% of the mapped land.
On 21% of Shelby 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: 27.29 in, 7.55 in below the 1991-2020 average year of 34.84 in.
USDA rates 77% 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 7 of the last 52 weeks; the most was 100% of its area, in 3 weeks, most recently on the August 4, 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
1 flood losses since 2016, $0 paid. The worst year was 2018, with 1.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 1 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 34.84 in |
| 12 months to August 2026 | 27.29 in (-7.55) |
| 2025 | 32.96 in (-1.88) |
| Wettest year since 1895 | 2015: 48.15 in |
| Driest year since 1895 | 1933: 20.02 in |
| Days with 1 inch or more, normal at HARLAN (3 mi away) | 8.4 |
Homes
| Housing units | 5,441 |
| Median year built | 1949 |
| Built before 1980 | 79% |
| Built 2000 or later | 10% |
| Owner-occupied | 78% |
| Median value, owner-occupied | $164,000 |
| Single-family detached | 87% |
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 |
|---|---|---|---|
| Audubon County, IA | 21 mi | 30% | 29% |
| Crawford County, IA | 25 mi | 12% | 15% |
| Pottawattamie County, IA | 26 mi | 14% | 25% |
| Harrison County, IA | 27 mi | 17% | 30% |
| Cass County, IA | 31 mi | 49% | 46% |
| Carroll County, IA | 34 mi | 18% | 41% |
| Guthrie County, IA | 42 mi | 62% | 66% |
| Monona County, IA | 42 mi | 30% | 46% |
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