Adams County, Illinois
A shallow water table limits basements on 70% of Adams County's mapped land, a higher share than 81% of US counties. Shrink-swell clay limits houses without basements on 36%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 39 flood losses here since 2016. 71% 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 Adams County
| Expansive clay (limits slab homes) | 36.3% |
| High water table (limits basements) | 69.5% |
| Septic fields very limited | 77.7% |
| Clay swell (LEP, by area) | 4.8% |
| High-swell land (LEP 6%+) | 35.3% |
| Mapped soil | 557,470 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Keswick | 6% | n/a |
| Bunkum | 6% | n/a |
| Keomah | 5% | n/a |
| Winfield | 5% | n/a |
| Wakeland | 5% | n/a |
| Timewell | 5% | n/a |
How we count · survey areas IL001 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 4.8% by land area here, and 35% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 36% of the mapped land.
On 70% of Adams 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: 37.92 in, 1.30 in below the 1991-2020 average year of 39.22 in.
USDA rates 78% 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 21 weeks, most recently on the March 10, 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
39 flood losses since 2016, $2.2 million paid. The worst year was 2019, with 37. Median water depth outside the building: 101 in.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 1 |
| 2019 | 37 |
| 2020 | 0 |
| 2021 | 1 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 39.22 in |
| 12 months to August 2026 | 37.92 in (-1.30) |
| 2025 | 29.43 in (-9.79) |
| Wettest year since 1895 | 1973: 58.10 in |
| Driest year since 1895 | 1953: 22.22 in |
| Days with 1 inch or more, normal at QUINCY RGNL AP (3 mi away) | 9.7 |
Homes
| Housing units | 30,302 |
| Median year built | 1965 |
| Built before 1980 | 71% |
| Built 2000 or later | 12% |
| Owner-occupied | 72% |
| Median value, owner-occupied | $162,600 |
| Single-family detached | 76% |
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 |
|---|---|---|---|
| Brown County, IL | 24 mi | 29% | 38% |
| Marion County, MO | 26 mi | 53% | 69% |
| Hancock County, IL | 29 mi | 48% | 72% |
| Lewis County, MO | 29 mi | 63% | 81% |
| Pike County, IL | 30 mi | 9% | 56% |
| Schuyler County, IL | 33 mi | 31% | 46% |
| Ralls County, MO | 35 mi | 56% | 75% |
| Clark County, MO | 41 mi | 58% | 78% |
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