Sinkhole risk in Brown 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: 37%
At or near the surface: 0%
Buried under cover: 37%

What to do about a house in Brown County

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

That works out to roughly 113 of Brown County's 306 square miles on soluble rock. With about 6,307 residents (21 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 315 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Brown County

The nearest county rated sinkhole country is Calhoun County, IL, about 55 miles south. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Schuyler County, IL 15 mi northeast · 0% at surface
Adams County, IL 24 mi west · under 1% at surface
Pike County, IL 24 mi south · 12% at surface
Scott County, IL 27 mi southeast · 0% at surface
Cass County, IL 27 mi east · 0% at surface
Morgan County, IL 33 mi southeast · 0% at surface

What Brown County is built on

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 24% of the county. Next is the Upper Valmeyeran (Aux Vases, Ste. Genevieve, St. Louis) Series at 7%.

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

Brown County ranks 30 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.