Sinkhole risk in Winnebago County, IL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 78%
At or near the surface: 5%
Buried under cover: 74%

What to do about a house in Winnebago County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 401 of Winnebago County's 513 square miles on soluble rock, 24 of them with the rock at or near the surface. With about 283,790 residents (553 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 358 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 74% under cover still counts, and the signs to look for and how an inspection works.

Counties around Winnebago County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 54 miles west. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Boone County, IL 17 mi east · 0% at surface
Ogle County, IL 22 mi south · 7% at surface
Rock County, WI 23 mi north · 0% at surface
Stephenson County, IL 26 mi west · 3% at surface
Green County, WI 33 mi northwest · 38% at surface
McHenry County, IL 36 mi east · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Galena-Platteville Groups (limestone), Ordovician in age, covering about 78% of the county.

Against the rest of Illinois

Winnebago County ranks 16 of 102 in Illinois for soluble rock at the surface, and sits above 62% of US counties on that measure.