Sinkhole risk in Rock Island 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: 47%
At or near the surface: 0%
Buried under cover: 47%

What to do about a house in Rock Island County

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

That works out to roughly 200 of Rock Island County's 427 square miles on soluble rock. With about 142,731 residents (334 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 311 map points about 1.2 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 47% under cover still counts.

Counties around Rock Island County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 64 miles north. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Scott County, IA 12 mi north · under 1% at surface
Mercer County, IL 20 mi southwest · 0% at surface
Henry County, IL 24 mi east · 0% at surface
Muscatine County, IA 28 mi west · 0% at surface
Clinton County, IA 30 mi north · 1% at surface
Cedar County, IA 36 mi northwest · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Silurian (dolostone (dolomite)), Silurian in age, covering about 24% of the county. Next is the Middle Devonian at 23%.

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

Rock Island County ranks 87 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.