Sinkhole risk in Stephenson 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: 80%
At or near the surface: 3%
Buried under cover: 77%

What this means before you buy

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 449 of Stephenson County's 564 square miles on soluble rock, 16 of them with the rock at or near the surface. With about 43,088 residents (76 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 390 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 77% under cover still counts, and the signs to look for and how an inspection works.

Counties around Stephenson County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 28 miles west, close enough that the same rock may run under the county line. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Green County, WI 23 mi north · 38% at surface
Carroll County, IL 23 mi southwest · 11% at surface
Winnebago County, IL 26 mi east · 5% at surface
Ogle County, IL 28 mi southeast · 7% at surface
Jo Daviess County, IL 28 mi west · 58% at surface
Lafayette County, WI 32 mi northwest · 91% at surface

The rock underneath

The largest mapped soluble unit here is the Galena-Platteville Groups (limestone), Ordovician in age, covering about 76% of the county. Next is the Silurian at 3%.

Against the rest of Illinois

Stephenson County ranks 17 of 102 in Illinois for soluble rock at the surface, and sits above 59% of US counties on that measure.