Piatt County, Illinois
A shallow water table limits basements on 94% of Piatt County's mapped land, a higher share than 98% of US counties and the 8th highest of 102 Illinois counties. Shrink-swell clay limits houses without basements on 57%.
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. 63% of homes were built before 1980, against 50% nationally; the median home dates from 1973.
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 Piatt County
| Expansive clay (limits slab homes) | 56.8% |
| High water table (limits basements) | 93.6% |
| Septic fields very limited | 96.0% |
| Clay swell (LEP, by area) | 5.3% |
| High-swell land (LEP 6%+) | 35.7% |
| Mapped soil | 281,015 acres |
How we count · survey areas IL147 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 5.3% by land area here, and 36% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 57% of the mapped land.
On 94% of Piatt 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: 39.51 in, 0.20 in above the 1991-2020 average year of 39.31 in.
USDA rates 96% 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 26 of the last 52 weeks; the most was 100% of its area, in 23 weeks, most recently on the March 24, 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 Piatt County since 2016.
Rain
| Average year, 1991-2020 | 39.31 in |
| 12 months to August 2026 | 39.51 in (+0.20) |
| 2025 | 26.75 in (-12.56) |
| Wettest year since 1895 | 1927: 54.65 in |
| Driest year since 1895 | 1914: 24.48 in |
| Days with 1 inch or more, normal at CHAMPAIGN 3S (19 mi away) | 9.8 |
Homes
| Housing units | 7,412 |
| Median year built | 1973 |
| Built before 1980 | 63% |
| Built 2000 or later | 17% |
| Owner-occupied | 85% |
| Median value, owner-occupied | $180,600 |
| Single-family detached | 87% |
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 |
|---|---|---|---|
| De Witt County, IL | 20 mi | 69% | 87% |
| Macon County, IL | 22 mi | 57% | 88% |
| Champaign County, IL | 23 mi | 26% | 94% |
| Moultrie County, IL | 26 mi | 68% | 89% |
| Douglas County, IL | 26 mi | 72% | 96% |
| McLean County, IL | 36 mi | 54% | 85% |
| Coles County, IL | 40 mi | 19% | 85% |
| Logan County, IL | 42 mi | 45% | 71% |
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