Grundy County, Illinois
A shallow water table limits basements on 85% of Grundy County's mapped land, a higher share than 92% of US counties. Shrink-swell clay limits houses without basements on 30%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 52 flood losses here since 2016, 38% of them in buildings with basements. 42% of homes were built before 1980, against 50% nationally; the median home dates from 1990.
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 Grundy County
| Expansive clay (limits slab homes) | 29.6% |
| High water table (limits basements) | 84.7% |
| Septic fields very limited | 95.7% |
| Clay swell (LEP, by area) | 4.7% |
| High-swell land (LEP 6%+) | 19.2% |
| Mapped soil | 275,355 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Drummer | 10% | over 99% |
| Reddick | 9% | n/a |
| Ashkum | 8% | n/a |
| Elliott | 7% | n/a |
| Selma | 6% | n/a |
| Brenton | 4% | n/a |
How we count · survey areas IL063 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 4.7% by land area here, and 19% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 30% of the mapped land.
On 85% of Grundy 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: 40.27 in, 2.60 in above the 1991-2020 average year of 37.67 in.
USDA rates 96% 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 20 of the last 52 weeks; the most was 100% of its area, on the June 2, 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
52 flood losses since 2016, $1.6 million paid. The worst year was 2020, with 27. Foundations of the buildings, where recorded: 38% basements, 31% slabs, 23% crawl spaces, 8% elevated. Median water depth outside the building: 14.5 in.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 1 |
| 2018 | 10 |
| 2019 | 11 |
| 2020 | 27 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 1 |
| 2024 | 1 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 37.67 in |
| 12 months to August 2026 | 40.27 in (+2.60) |
| 2025 | 30.83 in (-6.84) |
| Wettest year since 1895 | 1902: 52.60 in |
| Driest year since 1895 | 1963: 22.22 in |
| Days with 1 inch or more, normal at MORRIS 1 NW (6 mi away) | 9.5 |
Homes
| Housing units | 21,384 |
| Median year built | 1990 |
| Built before 1980 | 42% |
| Built 2000 or later | 36% |
| Owner-occupied | 74% |
| Median value, owner-occupied | $271,700 |
| Single-family detached | 72% |
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 |
|---|---|---|---|
| Kendall County, IL | 21 mi | 26% | 85% |
| Will County, IL | 24 mi | 24% | 85% |
| LaSalle County, IL | 25 mi | 37% | 84% |
| Livingston County, IL | 29 mi | 53% | 96% |
| Kankakee County, IL | 30 mi | 19% | 80% |
| DuPage County, IL | 42 mi | 33% | 90% |
| Kane County, IL | 45 mi | 8% | 82% |
| DeKalb County, IL | 46 mi | 28% | 98% |
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