Sinkhole risk in McHenry 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: 49%
At or near the surface: 0%
Buried under cover: 49%

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 296 of McHenry County's 603 square miles on soluble rock. With about 315,959 residents (524 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 384 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 49% under cover still counts, and how these percentages are measured.

Counties around McHenry County

The nearest county rated sinkhole country is Lafayette County, WI, about 89 miles west. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Boone County, IL 19 mi west · 0% at surface
Walworth County, WI 24 mi north · 0% at surface
Kane County, IL 27 mi south · 0% at surface
DeKalb County, IL 34 mi southwest · 0% at surface
Kenosha County, WI 34 mi northeast · 0% at surface
Lake County, IL 34 mi east · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Silurian (dolostone (dolomite)), Silurian in age, covering about 45% of the county. Next is the Galena-Platteville Groups at 4%.

Against the rest of Illinois

McHenry County ranks 69 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.