Benton County, Iowa
A shallow water table limits basements on 73% of Benton County's mapped land, a higher share than 84% of US counties. Shrink-swell clay limits houses without basements on 33%.
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. 64% of homes were built before 1980, against 50% nationally; the median home dates from 1964.
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 Benton County
| Expansive clay (limits slab homes) | 32.9% |
| High water table (limits basements) | 73.2% |
| Septic fields very limited | 97.4% |
| Clay swell (LEP, by area) | 4.3% |
| High-swell land (LEP 6%+) | 1.8% |
| Mapped soil | 459,800 acres |
How we count · survey areas IA011 (2025-09-08)
What the numbers mean here
Clay swell averages a linear extensibility of 4.3% by land area here, and 2% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 33% of the mapped land.
On 73% of Benton 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: 36.86 in, 0.01 in above the 1991-2020 average year of 36.85 in.
USDA rates 97% 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 17 of the last 52 weeks; the most was 93.6% of its area, in 4 weeks, most recently on the December 9, 2025 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, $649,726 paid. The worst year was 2016, with 27.
| Year | Flood losses |
|---|---|
| 2016 | 27 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 3 |
| 2020 | 1 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 1 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 36.85 in |
| 12 months to August 2026 | 36.86 in (+0.01) |
| 2025 | 32.67 in (-4.18) |
| Wettest year since 1895 | 1993: 57.32 in |
| Driest year since 1895 | 1988: 18.81 in |
| Days with 1 inch or more, normal at VINTON (6 mi away) | 9.6 |
Homes
| Housing units | 11,114 |
| Median year built | 1964 |
| Built before 1980 | 64% |
| Built 2000 or later | 16% |
| Owner-occupied | 85% |
| Median value, owner-occupied | $208,200 |
| Single-family detached | 89% |
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 |
|---|---|---|---|
| Linn County, IA | 24 mi | 9% | 57% |
| Tama County, IA | 24 mi | 42% | 49% |
| Iowa County, IA | 28 mi | 57% | 69% |
| Buchanan County, IA | 28 mi | 2% | 78% |
| Black Hawk County, IA | 29 mi | 9% | 75% |
| Poweshiek County, IA | 37 mi | 53% | 62% |
| Johnson County, IA | 38 mi | 40% | 56% |
| Grundy County, IA | 43 mi | 59% | 67% |
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