Low risk About 1% of Boone County's soil area is high shrink-swell (expansive) clay — far below the Illinois average of 25%, and far below the national average of 17%. That places it #100 of 102 Illinois counties for foundation soil risk.
Share of the county's ~176,865 acres of USDA-mapped soil with linear extensibility ≥ 6% in the top meter (SSURGO).
| High shrink-swell (expansive) clay | 1% |
| Moderately expansive | 89% |
| Low / non-expansive | 10% |
| Foundation risk tier | Low |
| Rank in Illinois | #100 of 102 counties |
| Higher-risk than | 24% of all U.S. counties |
Expansive clay swells as it takes on water and shrinks as it dries, and that repeated movement is what lifts and drops a foundation unevenly — opening stair-step cracks, racking door and window frames, and, left unmanaged, cracking slabs and footings. Boone County's exposure is minimal. With just 1% high-expansive soil, expansive clay is unlikely to be the main driver of foundation movement in Boone County. Settlement here more often traces to drainage, fill, tree roots, or original construction — worth a diagnosis before paying for clay fixes.
| County | High-risk soil | |
|---|---|---|
| Higher risk → | Whiteside County | 2% |
| This county | Boone County (#100 of 102) | 1% |
| Lower risk → | Hardin County | 1% |
For context, the average Illinois county is 25% high-expansive soil and the average U.S. county is 17%.
Foundation problems get more expensive the longer they wait. Get an assessment and repair quotes from independent local pros.
Get repair quotes →Costs follow the same structure everywhere — from a few hundred dollars for a single crack injection to $8,000–$25,000+ for pier stabilization on a settling home. At this risk level the clay is rarely the culprit, so a proper diagnosis is the first dollar to spend. See the full foundation repair cost guide for method-by-method pricing.
Risk metrics are computed from USDA SSURGO soil survey data (linear extensibility of soil components, area-weighted by county). Soil varies lot to lot — this is county-scale context, not a substitute for a site-specific geotechnical or structural assessment.