Sinkhole risk in Allen County, IN: 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: 90%
At or near the surface: 0%
Buried under cover: 90%

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 589 of Allen County's 657 square miles on soluble rock. With about 399,295 residents (608 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 397 map points about 1.3 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 90% under cover still counts, and how these percentages are measured.

Counties around Allen County

The nearest county rated sinkhole country is Monroe County, MI, about 100 miles northeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

DeKalb County, IN 21 mi north · 0% at surface
Whitley County, IN 23 mi west · 0% at surface
Adams County, IN 25 mi south · 0% at surface
Paulding County, OH 26 mi east · 0% at surface
Wells County, IN 26 mi south · under 1% at surface
Huntington County, IN 28 mi southwest · under 1% at surface

Which formation it is

The largest mapped soluble unit here is the Muscatatuck Group (limestone), Devonian in age, covering about 73% of the county. Next is the Wabash Formation at 17%.

Against the rest of Indiana

Allen County ranks 35 of 92 in Indiana for soluble rock at the surface, and sits above 0% of US counties on that measure.