DeKalb County, Illinois
A shallow water table limits basements on 98% of DeKalb County's mapped land, a higher share than 99% of US counties and the 2nd highest of 102 Illinois counties. Shrink-swell clay limits houses without basements on 28%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 7 flood losses here since 2016. 53% of homes were built before 1980, against 50% nationally; the median home dates from 1978.
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 DeKalb County
| Expansive clay (limits slab homes) | 27.6% |
| High water table (limits basements) | 97.6% |
| Septic fields very limited | 99.3% |
| Clay swell (LEP, by area) | 4.8% |
| High-swell land (LEP 6%+) | 15.0% |
| Mapped soil | 405,920 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Elpaso | 16% | n/a |
| Danabrook | 14% | n/a |
| Flanagan | 13% | n/a |
| Drummer | 12% | over 99% |
| Catlin | 11% | n/a |
| Parr | 3% | n/a |
How we count · survey areas IL037 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 4.8% by land area here, and 15% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 28% of the mapped land.
On 98% of DeKalb 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: 35.66 in, 1.84 in below the 1991-2020 average year of 37.50 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 15 of the last 52 weeks; the most was 100% of its area, in 2 weeks, most recently on the June 9, 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
7 flood losses since 2016, $51,370 paid. The worst year was 2020, with 3.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 1 |
| 2020 | 3 |
| 2021 | 2 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 37.50 in |
| 12 months to August 2026 | 35.66 in (-1.84) |
| 2025 | 30.81 in (-6.69) |
| Wettest year since 1895 | 1972: 48.85 in |
| Driest year since 1895 | 1901: 21.66 in |
| Days with 1 inch or more, normal at DE KALB (3 mi away) | 8.2 |
Homes
| Housing units | 41,678 |
| Median year built | 1978 |
| Built before 1980 | 53% |
| Built 2000 or later | 26% |
| Owner-occupied | 61% |
| Median value, owner-occupied | $243,600 |
| Single-family detached | 58% |
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 |
|---|---|---|---|
| Kane County, IL | 18 mi | 8% | 82% |
| Kendall County, IL | 27 mi | 26% | 85% |
| Lee County, IL | 29 mi | 14% | 66% |
| Boone County, IL | 29 mi | 6% | 55% |
| Ogle County, IL | 30 mi | 10% | 35% |
| McHenry County, IL | 34 mi | 2% | 54% |
| DuPage County, IL | 35 mi | 33% | 90% |
| Winnebago County, IL | 37 mi | 9% | 28% |
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