Sinkhole risk in Lee 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: 61%
At or near the surface: under 1%
Buried under cover: 60%

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 441 of Lee County's 725 square miles on soluble rock, 4 of them with the rock at or near the surface. With about 33,544 residents (46 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 365 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 60% under cover still counts, and how these percentages are measured.

Counties around Lee County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 63 miles northwest. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Ogle County, IL 20 mi north · 7% at surface
Bureau County, IL 27 mi southwest · 0% at surface
DeKalb County, IL 29 mi east · 0% at surface
Whiteside County, IL 32 mi west · under 1% at surface
LaSalle County, IL 35 mi southeast · 0% at surface
Putnam County, IL 38 mi south · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Galena-Platteville Groups (limestone), Ordovician in age, covering about 33% of the county. Next is the Prairie du Chien Group at 18%.

Against the rest of Illinois

Lee County ranks 24 of 102 in Illinois for soluble rock at the surface, and sits above 53% of US counties on that measure.