Sinkhole risk in Warren 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: 25%
At or near the surface: 0%
Buried under cover: 25%

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 134 of Warren County's 542 square miles on soluble rock. With about 16,217 residents (30 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 396 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and why the 25% under cover still counts.

Counties around Warren County

The nearest county rated sinkhole country is Jo Daviess County, IL, about 107 miles north. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Henderson County, IL 17 mi west · 0% at surface
Knox County, IL 22 mi east · 0% at surface
Mercer County, IL 25 mi north · 0% at surface
McDonough County, IL 27 mi south · under 1% at surface
Des Moines County, IA 30 mi west · 3% at surface
Fulton County, IL 34 mi southeast · 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 25% of the county.

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

Warren County ranks 97 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.