Sinkhole risk in Grundy 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: 10%
At or near the surface: 0%
Buried under cover: 10%

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 43 of Grundy County's 418 square miles on soluble rock. With about 53,835 residents (129 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 394 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 10% under cover still counts.

Counties around Grundy County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 119 miles northwest. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Kendall County, IL 20 mi north · 2% at surface
Will County, IL 24 mi northeast · 3% at surface
LaSalle County, IL 25 mi west · 0% at surface
Livingston County, IL 29 mi south · 0% at surface
Kankakee County, IL 30 mi east · 6% at surface
DuPage County, IL 42 mi northeast · 0% at surface

What Grundy County is built on

The largest mapped soluble unit here is the Galena-Platteville Groups (limestone), Ordovician in age, covering about 10% of the county.

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

Grundy County ranks 54 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.