Sinkhole risk in Alexander 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: 45%
At or near the surface: 31%
Buried under cover: 14%

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 105 of Alexander County's 235 square miles on soluble rock, 73 of them with the rock at or near the surface. With about 4,594 residents (20 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 492 map points about 0.7 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Alexander County

The nearest county rated sinkhole country is Union County, IL, about 22 miles north, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Alexander County stands out from its surroundings.

Pulaski County, IL 12 mi east · 7% at surface
Scott County, MO 15 mi southwest · 8% at surface
Ballard County, KY 21 mi southeast · 0% at surface
Union County, IL 22 mi north · 53% at surface
Cape Girardeau County, MO 23 mi northwest · 81% at surface
Mississippi County, MO 25 mi south · 0% at surface

What Alexander County is built on

The largest mapped soluble unit here is the Lower Devonian (limestone), Devonian in age, covering about 32% of the county. Next is the Silurian at 6%.

Against the rest of Illinois

Alexander County ranks 5 of 102 in Illinois for soluble rock at the surface, and sits above 80% of US counties on that measure.