Sinkhole risk in Jackson 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: 3%
At or near the surface: under 1%
Buried under cover: 3%

What this means before you buy

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 20 of Jackson County's 584 square miles on soluble rock, 5 of them with the rock at or near the surface. With about 53,199 residents (91 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 320 map points about 1.4 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 how these percentages are measured.

Counties around Jackson County

The nearest county rated sinkhole country is Union County, IL, about 22 miles south, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Perry County, IL 21 mi north · 0% at surface
Union County, IL 22 mi south · 53% at surface
Perry County, MO 24 mi west · 86% at surface
Williamson County, IL 25 mi east · 0% at surface
Franklin County, IL 29 mi northeast · 0% at surface
Randolph County, IL 30 mi northwest · under 1% at surface

What Jackson County is built on

The largest mapped soluble unit here is the Lower Devonian (limestone), Devonian in age, covering about 2% of the county. Next is the Lower Chesterian (Glen Dean - Renault) Series at 1%.

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

Jackson County ranks 20 of 102 in Illinois for soluble rock at the surface, and sits above 55% of US counties on that measure.