Hamilton County, Illinois
A shallow water table limits basements on 95% of Hamilton County's mapped land, a higher share than 99% of US counties and the 5th highest of 102 Illinois counties. Shrink-swell clay limits houses without basements on 23%.
97.2% of the county is in drought on the October 13, 2026 Drought Monitor map, up from 0% a week earlier. FEMA's flood data list no flood losses here since 2016. 61% of homes were built before 1980, against 50% nationally; the median home dates from 1970.
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) | 23.3% |
| High water table (limits basements) | 95.4% |
| Septic fields very limited | 98.2% |
| Clay swell (LEP, by area) | 4.4% |
| High-swell land (LEP 6%+) | 39.0% |
| Mapped soil | 279,070 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Bluford | 24% | 100% |
| Ava | 18% | n/a |
| Belknap | 13% | n/a |
| Bonnie | 8% | n/a |
| Zipp | 6% | n/a |
| Grantsburg | 6% | n/a |
How we count · survey areas IL065 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 4.4% by land area here, and 39% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 23% of the mapped land.
Clay shrinks as it dries: 97.2% of the county is in drought on the latest map, and 23% of Hamilton County's mapped land has shrink-swell clay.
On 95% 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: 31.55 in, 15.53 in below the 1991-2020 average year of 47.08 in.
USDA rates 98% of the land very limited for septic absorption fields.
Drought
97.2% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 19 of the last 52 weeks; the most was 100% of its area, in 6 weeks, most recently on the April 14, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 97.2% |
| 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 | 47.08 in |
| 12 months to August 2026 | 31.55 in (-15.53) |
| 2025 | 39.47 in (-7.61) |
| Wettest year since 1895 | 2011: 67.06 in |
| Driest year since 1895 | 1953: 27.82 in |
| Days with 1 inch or more, normal at CARMI 3 (19 mi away) | 13.6 |
Homes
| Housing units | 3,803 |
| Median year built | 1970 |
| Built before 1980 | 61% |
| Built 2000 or later | 15% |
| Owner-occupied | 76% |
| Median value, owner-occupied | $113,700 |
| Single-family detached | 77% |
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 |
|---|---|---|---|
| White County, IL | 20 mi | 12% | 75% |
| Franklin County, IL | 22 mi | 31% | 88% |
| Saline County, IL | 23 mi | 20% | 86% |
| Wayne County, IL | 25 mi | 26% | 94% |
| Jefferson County, IL | 26 mi | 26% | 87% |
| Gallatin County, IL | 27 mi | 31% | 67% |
| Williamson County, IL | 32 mi | 16% | 74% |
| Edwards County, IL | 35 mi | 21% | 92% |
Sources: USDA SSURGO (August 31, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status