Polk County, Iowa
A shallow water table limits basements on 52% of Polk County's mapped land, a higher share than 68% of US counties. Shrink-swell clay limits houses without basements on 13%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 202 flood losses here since 2016, 39% of them in buildings with basements. 49% of homes were built before 1980, against 50% nationally; the median home dates from 1982.
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 Polk County
| Expansive clay (limits slab homes) | 13.4% |
| High water table (limits basements) | 52.1% |
| Septic fields very limited | 63.9% |
| Clay swell (LEP, by area) | 3.7% |
| High-swell land (LEP 6%+) | 6.8% |
| Urban land, not rated | 8.3% |
| Mapped soil | 376,568 acres |
How we count · survey areas IA153 (2025-09-09)
What the numbers mean here
On 52% of Polk 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: 38.85 in, 3.06 in above the 1991-2020 average year of 35.79 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
202 flood losses since 2016, $12.4 million paid. The worst year was 2018, with 145. Foundations of the buildings, where recorded: 39% basements, 47% slabs, 4% crawl spaces, 10% elevated. Median water depth outside the building: 15 in.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 145 |
| 2019 | 21 |
| 2020 | 1 |
| 2021 | 3 |
| 2022 | 0 |
| 2023 | 1 |
| 2024 | 4 |
| 2025 | 1 |
| 2026 to date | 26 |
Rain
| Average year, 1991-2020 | 35.79 in |
| 12 months to August 2026 | 38.85 in (+3.06) |
| 2025 | 37.60 in (+1.81) |
| Wettest year since 1895 | 2010: 54.75 in |
| Driest year since 1895 | 1910: 18.83 in |
| Days with 1 inch or more, normal at ANKENY (5 mi away) | 9 |
Homes
| Housing units | 218,486 |
| Median year built | 1982 |
| Built before 1980 | 49% |
| Built 2000 or later | 31% |
| Owner-occupied | 67% |
| Median value, owner-occupied | $262,100 |
| Single-family detached | 63% |
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 |
|---|---|---|---|
| Warren County, IA | 24 mi | 81% | 80% |
| Dallas County, IA | 24 mi | 17% | 60% |
| Story County, IA | 25 mi | 9% | 64% |
| Jasper County, IA | 27 mi | 40% | 55% |
| Boone County, IA | 31 mi | 9% | 64% |
| Madison County, IA | 34 mi | 88% | 77% |
| Marion County, IA | 35 mi | 71% | 77% |
| Marshall County, IA | 39 mi | 42% | 47% |
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