Sinkhole risk in LaSalle County, IL: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 21%
At or near the surface: 0%
Buried under cover: 21%

The next step for one property

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 241 of LaSalle County's 1,135 square miles on soluble rock. With about 108,390 residents (95 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 306 map points about 1.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and why the 21% under cover still counts.

Counties around LaSalle County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 98 miles northwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Putnam County, IL 24 mi southwest · 0% at surface
Grundy County, IL 25 mi east · 0% at surface
Kendall County, IL 29 mi northeast · 2% at surface
Marshall County, IL 32 mi southwest · 0% at surface
Bureau County, IL 34 mi west · 0% at surface
Lee County, IL 35 mi northwest · under 1% at surface

The rock underneath

The largest mapped soluble unit here is the Prairie du Chien Group (dolostone (dolomite)), Ordovician in age, covering about 15% of the county. Next is the Galena-Platteville Groups at 7%.

The county also lies over the Illinois Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Illinois

LaSalle County ranks 65 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.