Boone County, Illinois
A shallow water table limits basements on 55% of Boone County's mapped land, a higher share than 71% of US counties. Shrink-swell clay limits houses without basements on 6%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 10 flood losses here since 2016. 45% of homes were built before 1980, against 50% nationally; the median home dates from 1986.
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 Boone County
| Expansive clay (limits slab homes) | 5.7% |
| High water table (limits basements) | 55.5% |
| Septic fields very limited | 73.7% |
| Clay swell (LEP, by area) | 4.3% |
| High-swell land (LEP 6%+) | 1.0% |
| Mapped soil | 180,490 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Drummer | 9% | over 99% |
| Pecatonica | 6% | n/a |
| Flagg | 5% | n/a |
| Sable | 4% | n/a |
| Kendall | 4% | n/a |
| Parr | 4% | n/a |
How we count · survey areas IL007 (2025-08-31)
What the numbers mean here
On 55% of Boone 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: 34.23 in, 3.13 in below the 1991-2020 average year of 37.36 in.
USDA rates 74% 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
10 flood losses since 2016, $94,558 paid. The worst year was 2017, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 2 |
| 2017 | 4 |
| 2018 | 2 |
| 2019 | 2 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 37.36 in |
| 12 months to August 2026 | 34.23 in (-3.13) |
| 2025 | 32.93 in (-4.43) |
| Wettest year since 1895 | 1972: 49.21 in |
| Driest year since 1895 | 1901: 19.88 in |
| Days with 1 inch or more, normal at HARVARD (12 mi away) | 8.1 |
Homes
| Housing units | 20,291 |
| Median year built | 1986 |
| Built before 1980 | 45% |
| Built 2000 or later | 28% |
| Owner-occupied | 82% |
| Median value, owner-occupied | $216,900 |
| Single-family detached | 78% |
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 |
|---|---|---|---|
| Winnebago County, IL | 17 mi | 9% | 28% |
| McHenry County, IL | 19 mi | 2% | 54% |
| Rock County, WI | 27 mi | 5% | 31% |
| Walworth County, WI | 28 mi | under 1% | 33% |
| DeKalb County, IL | 29 mi | 28% | 98% |
| Ogle County, IL | 32 mi | 10% | 35% |
| Kane County, IL | 33 mi | 8% | 82% |
| Stephenson County, IL | 43 mi | 13% | 24% |
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