McDonough County, Illinois
A shallow water table limits basements on 70% of McDonough County's mapped land, a higher share than 81% of US counties. Shrink-swell clay limits houses without basements on 63%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 72% of homes were built before 1980, against 50% nationally; the median home dates from 1965.
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 McDonough County
| Expansive clay (limits slab homes) | 63.2% |
| High water table (limits basements) | 69.5% |
| Septic fields very limited | 75.3% |
| Clay swell (LEP, by area) | 5.2% |
| High-swell land (LEP 6%+) | 42.0% |
| Mapped soil | 377,750 acres |
How we count · survey areas IL109 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 5.2% by land area here, and 42% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 63% of the mapped land.
On 70% of McDonough 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: 39.44 in, 0.17 in above the 1991-2020 average year of 39.27 in.
USDA rates 75% 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 25 of the last 52 weeks; the most was 100% of its area, in 20 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
FEMA's flood data list no flood losses in McDonough County since 2016.
Rain
| Average year, 1991-2020 | 39.27 in |
| 12 months to August 2026 | 39.44 in (+0.17) |
| 2025 | 28.93 in (-10.34) |
| Wettest year since 1895 | 2010: 52.65 in |
| Driest year since 1895 | 1901: 22.67 in |
| Days with 1 inch or more, normal at MACOMB (2 mi away) | 10.6 |
Homes
| Housing units | 13,587 |
| Median year built | 1965 |
| Built before 1980 | 72% |
| Built 2000 or later | 14% |
| Owner-occupied | 64% |
| Median value, owner-occupied | $107,500 |
| Single-family detached | 67% |
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 |
|---|---|---|---|
| Schuyler County, IL | 21 mi | 31% | 46% |
| Fulton County, IL | 25 mi | 24% | 38% |
| Hancock County, IL | 26 mi | 48% | 72% |
| Warren County, IL | 27 mi | 35% | 54% |
| Henderson County, IL | 28 mi | 13% | 43% |
| Brown County, IL | 34 mi | 29% | 38% |
| Cass County, IL | 41 mi | 13% | 45% |
| Knox County, IL | 41 mi | 41% | 41% |
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