Sinkhole risk in Boone 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: 75%
At or near the surface: 0%
Buried under cover: 75%

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 209 of Boone County's 281 square miles on soluble rock. With about 53,313 residents (190 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 400 map points about 0.8 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 75% under cover still counts, and how these percentages are measured.

Counties around Boone County

The nearest county rated sinkhole country is Lafayette County, WI, about 70 miles west. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Winnebago County, IL 17 mi west · 5% at surface
McHenry County, IL 19 mi east · 0% at surface
Rock County, WI 27 mi northwest · 0% at surface
Walworth County, WI 28 mi northeast · 0% at surface
DeKalb County, IL 29 mi south · 0% at surface
Ogle County, IL 32 mi southwest · 7% at surface

What Boone County is built on

The largest mapped soluble unit here is the Galena-Platteville Groups (limestone), Ordovician in age, covering about 74% of the county. Next is the Silurian at under 1%.

Against the rest of Illinois

Boone County ranks 29 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.