Low risk About 3% of Rock Island 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 #92 of 102 Illinois counties for foundation soil risk.
Share of the county's ~279,155 acres of USDA-mapped soil with linear extensibility ≥ 6% in the top meter (SSURGO).
| High shrink-swell (expansive) clay | 3% |
| Moderately expansive | 62% |
| Low / non-expansive | 35% |
| Foundation risk tier | Low |
| Rank in Illinois | #92 of 102 counties |
| Higher-risk than | 35% 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. Rock Island County's exposure is low-to-moderate. With just 3% high-expansive soil, expansive clay is unlikely to be the main driver of foundation movement in Rock Island County. Settlement here more often traces to drainage, fill, tree roots, or original construction — worth a diagnosis before paying for clay fixes.
Rock Island County's shrink-swell risk is concentrated in the Keomah soil series alongside Moline and Atlas — clays the USDA maps as strongly expansive, swelling and shrinking with every wet–dry cycle. Homes built on these series most need the drainage and moisture discipline above; a lot-level soil report (or the county NRCS survey) shows which one sits under a given address.
| County | High-risk soil | |
|---|---|---|
| Higher risk → | Putnam County | 3.8% |
| This county | Rock Island County (#92 of 102) | 3.1% |
| Lower risk → | Calhoun County | 2.6% |
For context, the average Illinois county is 25% high-expansive soil and the average U.S. county is 17%.
Foundation repair is one of the most over-sold jobs in home services — quotes for the same house can vary 3×. Before you sign anything, learn how to get honest bids and what a fair price looks like.
How to 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.