Iroquois County, Illinois
A shallow water table limits basements on 93% of Iroquois County's mapped land, a higher share than 97% of US counties and the 9th highest of 102 Illinois counties. Shrink-swell clay limits houses without basements on 44%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 206 flood losses here since 2016, 51% of them in buildings with basements. 78% of homes were built before 1980, against 50% nationally; the median home dates from 1960.
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 Iroquois County
| Expansive clay (limits slab homes) | 44.2% |
| High water table (limits basements) | 92.7% |
| Septic fields very limited | 99.0% |
| Clay swell (LEP, by area) | 5.3% |
| High-swell land (LEP 6%+) | 43.8% |
| Mapped soil | 715,925 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Milford | 16% | n/a |
| Bryce | 13% | n/a |
| Selma | 8% | n/a |
| Pella | 6% | n/a |
| Lisbon | 4% | n/a |
| Martinton | 4% | n/a |
How we count · survey areas IL075 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 5.3% by land area here, and 44% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 44% of the mapped land.
On 93% of Iroquois 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: 36.89 in, 1.90 in below the 1991-2020 average year of 38.79 in.
USDA rates 99% 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 26 of the last 52 weeks; the most was 100% of its area, in 11 weeks, most recently on the March 31, 2026 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
206 flood losses since 2016, $6.7 million paid. The worst year was 2018, with 201. Foundations of the buildings, where recorded: 51% basements, 9% slabs, 32% crawl spaces, 8% elevated. Median water depth outside the building: 18 in.
| Year | Flood losses |
|---|---|
| 2016 | 3 |
| 2017 | 0 |
| 2018 | 201 |
| 2019 | 0 |
| 2020 | 0 |
| 2021 | 2 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 38.79 in |
| 12 months to August 2026 | 36.89 in (-1.90) |
| 2025 | 30.46 in (-8.33) |
| Wettest year since 1895 | 1993: 55.62 in |
| Driest year since 1895 | 1963: 24.18 in |
| Days with 1 inch or more, normal at WATSEKA 2 NW (5 mi away) | 8.8 |
Homes
| Housing units | 12,789 |
| Median year built | 1960 |
| Built before 1980 | 78% |
| Built 2000 or later | 9% |
| Owner-occupied | 80% |
| Median value, owner-occupied | $137,800 |
| Single-family detached | 85% |
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 |
|---|---|---|---|
| Ford County, IL | 23 mi | 55% | 98% |
| Newton County, IN | 27 mi | 4% | 88% |
| Kankakee County, IL | 27 mi | 19% | 80% |
| Benton County, IN | 29 mi | 2% | 95% |
| Warren County, IN | 36 mi | 5% | 82% |
| Livingston County, IL | 39 mi | 53% | 96% |
| Vermilion County, IL | 39 mi | 34% | 90% |
| Jasper County, IN | 42 mi | 5% | 86% |
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