Sangamon County, Illinois
A shallow water table limits basements on 72% of Sangamon County's mapped land, a higher share than 83% of US counties. Shrink-swell clay limits houses without basements on 58%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 15 flood losses here since 2016. 62% of homes were built before 1980, against 50% nationally; the median home dates from 1974.
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 Sangamon County
| Expansive clay (limits slab homes) | 57.8% |
| High water table (limits basements) | 71.8% |
| Septic fields very limited | 73.8% |
| Clay swell (LEP, by area) | 5.3% |
| High-swell land (LEP 6%+) | 38.3% |
| Mapped soil | 560,755 acres |
How we count · survey areas IL167 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 5.3% by land area here, and 38% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 58% of the mapped land.
On 72% of Sangamon 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: 38.03 in, 0.78 in below the 1991-2020 average year of 38.81 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 24 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 | 10% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
15 flood losses since 2016, $387,557 paid. The worst year was 2020, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 2 |
| 2017 | 0 |
| 2018 | 0 |
| 2019 | 4 |
| 2020 | 4 |
| 2021 | 0 |
| 2022 | 2 |
| 2023 | 1 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 38.81 in |
| 12 months to August 2026 | 38.03 in (-0.78) |
| 2025 | 27.03 in (-11.78) |
| Wettest year since 1895 | 2008: 52.32 in |
| Driest year since 1895 | 1914: 24.04 in |
| Days with 1 inch or more, normal at SPRINGFIELD CAPITAL AP (6 mi away) | 8.7 |
Homes
| Housing units | 93,382 |
| Median year built | 1974 |
| Built before 1980 | 62% |
| Built 2000 or later | 16% |
| Owner-occupied | 71% |
| Median value, owner-occupied | $176,300 |
| Single-family detached | 73% |
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 |
|---|---|---|---|
| Menard County, IL | 20 mi | 27% | 51% |
| Christian County, IL | 25 mi | 72% | 86% |
| Morgan County, IL | 29 mi | 43% | 54% |
| Logan County, IL | 30 mi | 45% | 71% |
| Cass County, IL | 34 mi | 13% | 45% |
| Mason County, IL | 36 mi | 3% | 42% |
| Macoupin County, IL | 37 mi | 62% | 78% |
| Montgomery County, IL | 38 mi | 68% | 88% |
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