Sinkhole risk in Oconto County, WI: 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: 38%
At or near the surface: under 1%
Buried under cover: 37%

The next step for one property

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

That works out to roughly 374 of Oconto County's 997 square miles on soluble rock, 4 of them with the rock at or near the surface. With about 40,037 residents (40 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 472 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 the 37% under cover still counts, and how these percentages are measured.

Counties around Oconto County

The nearest county rated sinkhole country is Oceana County, MI, about 129 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Menominee County, WI 23 mi west · 0% at surface
Marinette County, WI 26 mi northeast · 0% at surface
Shawano County, WI 30 mi southwest · 0% at surface
Brown County, WI 38 mi south · under 1% at surface
Outagamie County, WI 42 mi south · 0% at surface
Langlade County, WI 46 mi northwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Prairie du Chien Group (shale), Lower Ordovician in age, covering about 19% of the county. Next is the Sinnipee Group at 15%.

Against the rest of Wisconsin

Oconto County ranks 20 of 72 in Wisconsin for soluble rock at the surface, and sits above 52% of US counties on that measure.