Sinkhole risk in Henderson 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: 55%
At or near the surface: 0%
Buried under cover: 55%

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 208 of Henderson County's 379 square miles on soluble rock. With about 6,048 residents (16 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 255 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why gypsum and salt move faster than limestone, and why the 55% under cover still counts.

Counties around Henderson County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 113 miles north. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Des Moines County, IA 15 mi northwest · 3% at surface
Warren County, IL 17 mi east · 0% at surface
McDonough County, IL 28 mi southeast · under 1% at surface
Mercer County, IL 29 mi north · 0% at surface
Lee County, IA 30 mi west · 2% at surface
Hancock County, IL 31 mi southwest · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Lower Valmeyeran (Keokuk-Sedalia) Series (limestone), Mississippian in age, covering about 46% of the county. Next is the Middle Devonian at 8%.

The county also lies over the Illinois Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Illinois

Henderson County ranks 57 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.