St. Clair County, IL Shrink-Swell Risk

St. Clair County, IL's soil, for shrink-swell risk

Moderate

St. Clair County, IL: USDA's soil survey rates 76% of the county "Moderate" for shrink-swell potential (4.28% linear extensibility). That's a middle reading: not the sharp swings that crack a foundation outright, but enough that grading and drainage are worth getting right.

What St. Clair County's reading doesn't cover

Two lots a mile apart in St. Clair County can carry different soil, even though they share one countywide reading. A local geotechnical report, typically $1,000-$5,000 (around $2,700 typical), is the only way to know what one lot in St. Clair County will actually do.

What it costs to find out, versus to ignore it

With St. Clair County, IL rating "Moderate", a geotechnical report is still worthwhile before a build, just less urgent than in a high-risk county. A geotechnical report runs $1,000-$5,000, typically around $2,700. Foundation repair, if a specific lot turns out to differ from the county average, runs $5,000-$15,000.

Where this sits nationally

Nationally, St. Clair County, IL is the 445-most-constrained of 3,085 rated counties for shrink-swell soil. Within Illinois alone it ranks 15 of 101. St. Clair County covers 658 square miles and counts 251,149 residents.

For contrast

Orleans Parish, LA carries this site's most-constrained reading. Dale County, AL and Lincoln County, KY are worth a look for comparison.

How this reading is built, and its real limits · Moisture management: the cheap fix that works on any soil

More of Illinois

Every county in Illinois is on this site, including Kane County, IL and Stark County, IL. The full underlying dataset is downloadable directly, one row per county.