Dallas County, Iowa
A shallow water table limits basements on 60% of Dallas County's mapped land, a higher share than 74% of US counties. Shrink-swell clay limits houses without basements on 17%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 7 flood losses here since 2016. 22% of homes were built before 1980, against 50% nationally; the median home dates from 2006.
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 Dallas County
| Expansive clay (limits slab homes) | 16.6% |
| High water table (limits basements) | 59.6% |
| Septic fields very limited | 64.3% |
| Clay swell (LEP, by area) | 3.7% |
| High-swell land (LEP 6%+) | 12.2% |
| Mapped soil | 378,200 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Clarion | 29% | 61% |
| Canisteo | 11% | 100% |
| Nicollet | 10% | n/a |
| Webster | 8% | 100% |
| Storden | 5% | n/a |
| Sharpsburg | 4% | 93% |
How we count · survey areas IA049 (2025-09-08)
What the numbers mean here
Clay swell averages a linear extensibility of 3.7% by land area here, and 12% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 17% of the mapped land.
On 60% of Dallas 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: 37.71 in, 2.38 in above the 1991-2020 average year of 35.33 in.
USDA rates 64% 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. No part of the county was in drought in the last 52 weeks.
| 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
7 flood losses since 2016, $335,490 paid. The worst year was 2018, with 3.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 3 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 2 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 35.33 in |
| 12 months to August 2026 | 37.71 in (+2.38) |
| 2025 | 38.32 in (+2.99) |
| Wettest year since 1895 | 2010: 50.40 in |
| Driest year since 1895 | 1930: 19.50 in |
| Days with 1 inch or more, normal at PERRY (11 mi away) | 8.1 |
Homes
| Housing units | 44,804 |
| Median year built | 2006 |
| Built before 1980 | 22% |
| Built 2000 or later | 65% |
| Owner-occupied | 69% |
| Median value, owner-occupied | $355,600 |
| Single-family detached | 62% |
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 |
|---|---|---|---|
| Guthrie County, IA | 24 mi | 62% | 66% |
| Polk County, IA | 24 mi | 13% | 52% |
| Madison County, IA | 24 mi | 88% | 77% |
| Boone County, IA | 25 mi | 9% | 64% |
| Greene County, IA | 31 mi | 11% | 71% |
| Adair County, IA | 33 mi | 91% | 80% |
| Warren County, IA | 34 mi | 81% | 80% |
| Story County, IA | 38 mi | 9% | 64% |
Sources: USDA SSURGO (September 8, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status