Sinkhole risk in Waukesha 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: 99%
At or near the surface: 0%
Buried under cover: 99%

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 541 of Waukesha County's 550 square miles on soluble rock. With about 417,029 residents (759 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 391 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 99% under cover still counts, and how these percentages are measured.

Counties around Waukesha County

The nearest county rated sinkhole country is Iowa County, WI, about 92 miles west. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Milwaukee County, WI 24 mi east · 0% at surface
Jefferson County, WI 24 mi west · 3% at surface
Washington County, WI 26 mi north · 0% at surface
Walworth County, WI 27 mi southwest · 0% at surface
Racine County, WI 32 mi southeast · 0% at surface
Dodge County, WI 35 mi northwest · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Silurian, undivided (dolostone (dolomite)), Silurian in age, covering about 58% of the county. Next is the Sinnipee Group at 22%.

Against the rest of Wisconsin

Waukesha County ranks 69 of 72 in Wisconsin for soluble rock at the surface, and sits above 0% of US counties on that measure.