Sinkhole risk in Hardin County, OH: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 100%
At or near the surface: 0%
Buried under cover: 100%

What this means before you buy

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 470 of Hardin County's 470 square miles on soluble rock. With about 30,402 residents (65 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 349 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 100% under cover still counts, and the signs to look for and how an inspection works.

Counties around Hardin County

The nearest county rated sinkhole country is Monroe County, MI, about 87 miles north. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Logan County, OH 20 mi south · 0% at surface
Wyandot County, OH 22 mi northeast · 0% at surface
Hancock County, OH 23 mi north · 0% at surface
Allen County, OH 24 mi west · 0% at surface
Marion County, OH 26 mi east · 0% at surface
Union County, OH 30 mi southeast · 0% at surface

What Hardin County is built on

The largest mapped soluble unit here is the Tymochtee and Greenfield Formations, Undivided (dolostone (dolomite)), Silurian in age, covering about 65% of the county. Next is the Salina Group at 30%.

Against the rest of Ohio

Hardin County ranks 38 of 88 in Ohio for soluble rock at the surface, and sits above 0% of US counties on that measure.