LaSalle County, Illinois
A shallow water table limits basements on 84% of LaSalle County's mapped land, a higher share than 92% of US counties. Shrink-swell clay limits houses without basements on 37%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 27 flood losses here since 2016. 70% of homes were built before 1980, against 50% nationally; the median home dates from 1963.
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 LaSalle County
| Expansive clay (limits slab homes) | 37.0% |
| High water table (limits basements) | 84.3% |
| Septic fields very limited | 93.4% |
| Clay swell (LEP, by area) | 5.1% |
| High-swell land (LEP 6%+) | 23.2% |
| Mapped soil | 735,640 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Muscatune | 9% | n/a |
| Drummer | 8% | over 99% |
| Sable | 7% | n/a |
| Catlin | 6% | n/a |
| Rutland | 5% | n/a |
| Flanagan | 4% | n/a |
How we count · survey areas IL099 (2025-08-31)
What the numbers mean here
Clay swell averages a linear extensibility of 5.1% by land area here, and 23% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 37% of the mapped land.
On 84% of LaSalle 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: 39.90 in, 2.77 in above the 1991-2020 average year of 37.13 in.
USDA rates 93% 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 6 weeks, most recently on the November 25, 2025 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
27 flood losses since 2016, $629,582 paid. The worst year was 2020, with 9.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 2 |
| 2018 | 5 |
| 2019 | 6 |
| 2020 | 9 |
| 2021 | 2 |
| 2022 | 2 |
| 2023 | 0 |
| 2024 | 0 |
| 2025 | 0 |
| 2026 to date | 1 |
Rain
| Average year, 1991-2020 | 37.13 in |
| 12 months to August 2026 | 39.90 in (+2.77) |
| 2025 | 29.94 in (-7.19) |
| Wettest year since 1895 | 2019: 52.65 in |
| Driest year since 1895 | 1956: 22.25 in |
| Days with 1 inch or more, normal at OTTAWA 5SW (2 mi away) | 8.3 |
Homes
| Housing units | 49,843 |
| Median year built | 1963 |
| Built before 1980 | 70% |
| Built 2000 or later | 13% |
| Owner-occupied | 74% |
| Median value, owner-occupied | $161,900 |
| Single-family detached | 79% |
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 |
|---|---|---|---|
| Putnam County, IL | 24 mi | 23% | 50% |
| Grundy County, IL | 25 mi | 30% | 85% |
| Kendall County, IL | 29 mi | 26% | 85% |
| Marshall County, IL | 32 mi | 36% | 66% |
| Bureau County, IL | 34 mi | 25% | 53% |
| Lee County, IL | 35 mi | 14% | 66% |
| Livingston County, IL | 36 mi | 53% | 96% |
| DeKalb County, IL | 39 mi | 28% | 98% |
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