Sinkhole risk in Putnam 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 483 of Putnam County's 483 square miles on soluble rock. With about 34,206 residents (71 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 331 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 Putnam County

The nearest county rated sinkhole country is Monroe County, MI, about 70 miles northeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Allen County, OH 18 mi south · 0% at surface
Henry County, OH 21 mi north · 0% at surface
Hancock County, OH 24 mi east · 0% at surface
Paulding County, OH 24 mi west · 0% at surface
Van Wert County, OH 27 mi southwest · 0% at surface
Defiance County, OH 28 mi northwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Salina Group (dolostone (dolomite)), Silurian in age, covering about 98% of the county. Next is the Tymochtee and Greenfield Formations, Undivided at 2%.

Against the rest of Ohio

Putnam County ranks 69 of 88 in Ohio for soluble rock at the surface, and sits above 0% of US counties on that measure.