Carroll County, Illinois
A shallow water table limits basements on 17% of Carroll County's mapped land. Shrink-swell clay limits houses without basements on 13%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 2 flood losses here since 2016. 71% of homes were built before 1980, against 50% nationally; the median home dates from 1957.
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 Carroll County
| Expansive clay (limits slab homes) | 13.3% |
| High water table (limits basements) | 17.3% |
| Septic fields very limited | 46.1% |
| Clay swell (LEP, by area) | 4.0% |
| High-swell land (LEP 6%+) | 8.1% |
| Mapped soil | 298,535 acres |
How we count · survey areas IL015 (2025-09-01)
What the numbers mean here
On 17% of Carroll 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: 30.60 in, 7.73 in below the 1991-2020 average year of 38.33 in.
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 27 of the last 52 weeks; the most was 100% of its area, in 11 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
2 flood losses since 2016, $0 paid. The worst year was 2019, with 1.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 1 |
| 2019 | 1 |
| 2020 | 0 |
| 2021 | 0 |
| 2022 | 0 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 38.33 in |
| 12 months to August 2026 | 30.60 in (-7.73) |
| 2025 | 31.84 in (-6.49) |
| Wettest year since 1895 | 2019: 51.70 in |
| Driest year since 1895 | 1910: 19.49 in |
| Days with 1 inch or more, normal at MT CARROLL (4 mi away) | 10.4 |
Homes
| Housing units | 8,204 |
| Median year built | 1957 |
| Built before 1980 | 71% |
| Built 2000 or later | 11% |
| Owner-occupied | 77% |
| Median value, owner-occupied | $114,500 |
| Single-family detached | 86% |
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 |
|---|---|---|---|
| Whiteside County, IL | 22 mi | 2% | 40% |
| Stephenson County, IL | 23 mi | 13% | 24% |
| Jo Daviess County, IL | 25 mi | 17% | 20% |
| Ogle County, IL | 31 mi | 10% | 35% |
| Clinton County, IA | 34 mi | 15% | 44% |
| Jackson County, IA | 34 mi | 1% | 18% |
| Lee County, IL | 39 mi | 14% | 66% |
| Lafayette County, WI | 42 mi | 29% | 14% |
Sources: USDA SSURGO (September 1, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status