Hamilton County, Iowa
A shallow water table limits basements on 91% of Hamilton County's mapped land, a higher share than 96% of US counties and the 3rd highest of 99 Iowa counties. Shrink-swell clay limits houses without basements on 32%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 79% of homes were built before 1980, against 50% nationally; the median home dates from 1953.
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 Hamilton County
| Expansive clay (limits slab homes) | 32.5% |
| High water table (limits basements) | 90.8% |
| Septic fields very limited | 94.0% |
| Clay swell (LEP, by area) | 4.9% |
| High-swell land (LEP 6%+) | 30.1% |
| Mapped soil | 369,600 acres |
How we count · survey areas IA079 (2025-09-08)
What the numbers mean here
Clay swell averages a linear extensibility of 4.9% by land area here, and 30% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 32% of the mapped land.
On 91% of Hamilton 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: 37.94 in, 1.93 in above the 1991-2020 average year of 36.01 in.
USDA rates 94% 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
FEMA's flood data list no flood losses in Hamilton County since 2016.
Rain
| Average year, 1991-2020 | 36.01 in |
| 12 months to August 2026 | 37.94 in (+1.93) |
| 2025 | 41.37 in (+5.36) |
| Wettest year since 1895 | 1993: 54.67 in |
| Driest year since 1895 | 1910: 19.42 in |
| Days with 1 inch or more, normal at WEBSTER CITY (7 mi away) | 9.3 |
Homes
| Housing units | 7,040 |
| Median year built | 1953 |
| Built before 1980 | 79% |
| Built 2000 or later | 8% |
| Owner-occupied | 73% |
| Median value, owner-occupied | $156,400 |
| Single-family detached | 81% |
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 |
|---|---|---|---|
| Wright County, IA | 24 mi | 27% | 89% |
| Hardin County, IA | 24 mi | 17% | 57% |
| Webster County, IA | 24 mi | 27% | 88% |
| Boone County, IA | 27 mi | 9% | 64% |
| Story County, IA | 27 mi | 9% | 64% |
| Franklin County, IA | 33 mi | 13% | 72% |
| Humboldt County, IA | 37 mi | 10% | 90% |
| Greene County, IA | 42 mi | 11% | 71% |
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