Sinkhole risk in Morgan 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: 7%
At or near the surface: 0%
Buried under cover: 7%

What to do about a house in Morgan County

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

That works out to roughly 40 of Morgan County's 569 square miles on soluble rock. With about 32,618 residents (57 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 257 map points about 1.5 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 7% under cover still counts.

Counties around Morgan County

The nearest county rated sinkhole country is Calhoun County, IL, about 45 miles southwest. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Scott County, IL 16 mi west · 0% at surface
Cass County, IL 18 mi north · 0% at surface
Greene County, IL 27 mi south · 0% at surface
Sangamon County, IL 29 mi east · 0% at surface
Menard County, IL 30 mi northeast · 0% at surface
Brown County, IL 33 mi northwest · 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 5% of the county. Next is the Middle Valmeyeran (Salem, Warsaw, Borden, Springville; includes thin Mvl and Mk in south and east) Series at 2%.

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

Morgan County ranks 80 of 102 in Illinois for soluble rock at the surface, and sits above 0% of US counties on that measure.