SinkholeOdds

Sinkhole risk in Mercer 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
17%
At or near the surface
0%
Buried under cover
17%

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 97 of Mercer County's 561 square miles on soluble rock. With about 15,292 residents (27 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 348 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and why the 17% under cover still counts.

Counties around Mercer County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 84 miles north. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

The rock underneath

The largest mapped soluble unit here is the Middle Devonian (limestone), Devonian in age, covering about 16% of the county. Next is the Cedar Valley Limestone at 1%.

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

Mercer County ranks 78 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.