Sinkhole risk in Milwaukee 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: 97%
At or near the surface: 0%
Buried under cover: 97%

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 235 of Milwaukee County's 241 square miles on soluble rock. With about 924,740 residents (3,830 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 326 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 97% under cover still counts, and how these percentages are measured.

Counties around Milwaukee County

The nearest county rated sinkhole country is Muskegon County, MI, about 81 miles northeast. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Racine County, WI 10 mi southeast · 0% at surface
Kenosha County, WI 22 mi south · 0% at surface
Waukesha County, WI 24 mi west · 0% at surface
Washington County, WI 38 mi northwest · 0% at surface
Walworth County, WI 38 mi southwest · 0% at surface
Ozaukee County, WI 41 mi north · 0% at surface

What Milwaukee County is built on

The largest mapped soluble unit here is the Silurian, undivided (dolostone (dolomite)), Silurian in age, covering about 80% of the county. Next is the Traverse Group at 17%.

Against the rest of Wisconsin

Milwaukee County ranks 51 of 72 in Wisconsin for soluble rock at the surface, and sits above 0% of US counties on that measure.