McHenry County, Illinois
A shallow water table limits basements on 54% of McHenry County's mapped land, a higher share than 70% of US counties. Shrink-swell clay limits houses without basements on 2%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 152 flood losses here since 2016, 26% of them in buildings with basements. 38% of homes were built before 1980, against 50% nationally; the median home dates from 1989.
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 McHenry County
| Expansive clay (limits slab homes) | 2.2% |
| High water table (limits basements) | 53.8% |
| Septic fields very limited | 91.8% |
| Clay swell (LEP, by area) | 4.1% |
| High-swell land (LEP 6%+) | 2.0% |
| Mapped soil | 391,220 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Kidder | 6% | n/a |
| Pella | 6% | n/a |
| Kidami | 6% | n/a |
| Ringwood | 5% | n/a |
| Houghton | 4% | n/a |
| Fox | 4% | 1% |
How we count · survey areas IL111 (2025-08-31)
What the numbers mean here
On 54% of McHenry 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: 38.55 in, 1.14 in above the 1991-2020 average year of 37.41 in.
USDA rates 92% 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 9 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
152 flood losses since 2016, $2.2 million paid. The worst year was 2017, with 91. Foundations of the buildings, where recorded: 26% basements, 14% slabs, 52% crawl spaces, 8% elevated. Median water depth outside the building: 10 in.
| Year | Flood losses |
|---|---|
| 2016 | 1 |
| 2017 | 91 |
| 2018 | 8 |
| 2019 | 4 |
| 2020 | 10 |
| 2021 | 1 |
| 2022 | 2 |
| 2023 | 1 |
| 2024 | 2 |
| 2025 | 0 |
| 2026 to date | 32 |
Rain
| Average year, 1991-2020 | 37.41 in |
| 12 months to August 2026 | 38.55 in (+1.14) |
| 2025 | 32.18 in (-5.23) |
| Wettest year since 1895 | 2019: 48.85 in |
| Driest year since 1895 | 1901: 20.03 in |
| Days with 1 inch or more, normal at MC HENRY -WG STRATTON L&D (10 mi away) | 8.5 |
Homes
| Housing units | 121,329 |
| Median year built | 1989 |
| Built before 1980 | 38% |
| Built 2000 or later | 26% |
| Owner-occupied | 83% |
| Median value, owner-occupied | $308,100 |
| 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 |
|---|---|---|---|
| Boone County, IL | 19 mi | 6% | 55% |
| Walworth County, WI | 24 mi | under 1% | 33% |
| Kane County, IL | 27 mi | 8% | 82% |
| DeKalb County, IL | 34 mi | 28% | 98% |
| Kenosha County, WI | 34 mi | 15% | 76% |
| Lake County, IL | 34 mi | 16% | 87% |
| Winnebago County, IL | 36 mi | 9% | 28% |
| DuPage County, IL | 38 mi | 33% | 90% |
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