Sinkhole risk in Jefferson 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: 88%
At or near the surface: 3%
Buried under cover: 86%

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 491 of Jefferson County's 556 square miles on soluble rock, 14 of them with the rock at or near the surface. With about 86,245 residents (155 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 391 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 86% under cover still counts, and how these percentages are measured.

Counties around Jefferson County

The nearest county rated sinkhole country is Iowa County, WI, about 69 miles west. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Waukesha County, WI 24 mi east · 0% at surface
Walworth County, WI 27 mi southeast · 0% at surface
Rock County, WI 28 mi southwest · 0% at surface
Dodge County, WI 29 mi north · 0% at surface
Dane County, WI 33 mi west · 19% at surface
Washington County, WI 38 mi northeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Sinnipee Group (dolostone (dolomite)), Ordovician in age, covering about 46% of the county. Next is the Ancell Group at 20%.

Against the rest of Wisconsin

Jefferson County ranks 16 of 72 in Wisconsin for soluble rock at the surface, and sits above 59% of US counties on that measure.