Sinkhole risk in Hancock 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: 94%
At or near the surface: 0%
Buried under cover: 94%

What to do about a house in Hancock 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 744 of Hancock County's 794 square miles on soluble rock. With about 17,008 residents (21 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 333 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Hancock County

The nearest county rated sinkhole country is Calhoun County, IL, about 90 miles south. None of the 6 closest counties land in the same band, so Hancock County stands out from its surroundings.

Lee County, IA 23 mi northwest · 2% at surface
McDonough County, IL 26 mi east · under 1% at surface
Adams County, IL 29 mi south · under 1% at surface
Clark County, MO 30 mi west · 0% at surface
Henderson County, IL 31 mi northeast · 0% at surface
Schuyler County, IL 34 mi southeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series (limestone), Mississippian in age, covering about 38% of the county. Next is the Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series at 38%.

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

Hancock County ranks 56 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.