Radon levels in Wisconsin

Verified county-level radon indicators are available for 72 Wisconsin counties. Select a county for its source period and sample details.

High results are most common in Langlade County (59%) and least common in Ashland County (10%)Share of tests at or above 4 pCi/L by county · Wisconsin county radon test results, 2005–2017 · 72 of 72 counties have data
Adams County: 18% of tests at or above 4 pCi/L · 573 testsAshland County: 10% of tests at or above 4 pCi/L · 770 testsBarron County: 46% of tests at or above 4 pCi/L · 1,156 testsBayfield County: 24% of tests at or above 4 pCi/L · 514 testsBrown County: 42% of tests at or above 4 pCi/L · 5,290 testsBuffalo County: 51% of tests at or above 4 pCi/L · 532 testsBurnett County: 23% of tests at or above 4 pCi/L · 430 testsCalumet County: 47% of tests at or above 4 pCi/L · 1,529 testsChippewa County: 49% of tests at or above 4 pCi/L · 2,202 testsClark County: 29% of tests at or above 4 pCi/L · 610 testsColumbia County: 35% of tests at or above 4 pCi/L · 1,405 testsCrawford County: 54% of tests at or above 4 pCi/L · 911 testsDane County: 38% of tests at or above 4 pCi/L · 18,790 testsDodge County: 54% of tests at or above 4 pCi/L · 2,208 testsDoor County: 42% of tests at or above 4 pCi/L · 2,552 testsDouglas County: 14% of tests at or above 4 pCi/L · 639 testsDunn County: 43% of tests at or above 4 pCi/L · 1,395 testsEau Claire County: 36% of tests at or above 4 pCi/L · 3,519 testsFlorence County: 39% of tests at or above 4 pCi/L · 435 testsFond du Lac County: 49% of tests at or above 4 pCi/L · 2,913 testsForest County: 37% of tests at or above 4 pCi/L · 770 testsGrant County: 59% of tests at or above 4 pCi/L · 2,375 testsGreen County: 53% of tests at or above 4 pCi/L · 1,138 testsGreen Lake County: 46% of tests at or above 4 pCi/L · 847 testsIowa County: 55% of tests at or above 4 pCi/L · 1,172 testsIron County: 25% of tests at or above 4 pCi/L · 281 testsJackson County: 34% of tests at or above 4 pCi/L · 525 testsJefferson County: 39% of tests at or above 4 pCi/L · 2,157 testsJuneau County: 16% of tests at or above 4 pCi/L · 774 testsKenosha County: 46% of tests at or above 4 pCi/L · 5,790 testsKewaunee County: 46% of tests at or above 4 pCi/L · 431 testsLa Crosse County: 36% of tests at or above 4 pCi/L · 5,408 testsLafayette County: 56% of tests at or above 4 pCi/L · 528 testsLanglade County: 59% of tests at or above 4 pCi/L · 1,243 testsLincoln County: 37% of tests at or above 4 pCi/L · 1,137 testsManitowoc County: 32% of tests at or above 4 pCi/L · 1,824 testsMarathon County: 57% of tests at or above 4 pCi/L · 6,659 testsMarinette County: 24% of tests at or above 4 pCi/L · 1,540 testsMarquette County: 13% of tests at or above 4 pCi/L · 540 testsMenominee County: 35% of tests at or above 4 pCi/L · 130 testsMilwaukee County: 33% of tests at or above 4 pCi/L · 20,170 testsMonroe County: 23% of tests at or above 4 pCi/L · 1,591 testsOconto County: 43% of tests at or above 4 pCi/L · 894 testsOneida County: 29% of tests at or above 4 pCi/L · 2,848 testsOutagamie County: 46% of tests at or above 4 pCi/L · 5,789 testsOzaukee County: 39% of tests at or above 4 pCi/L · 4,401 testsPepin County: 46% of tests at or above 4 pCi/L · 322 testsPierce County: 47% of tests at or above 4 pCi/L · 1,523 testsPolk County: 38% of tests at or above 4 pCi/L · 1,369 testsPortage County: 48% of tests at or above 4 pCi/L · 2,253 testsPrice County: 28% of tests at or above 4 pCi/L · 845 testsRacine County: 46% of tests at or above 4 pCi/L · 6,151 testsRichland County: 28% of tests at or above 4 pCi/L · 1,025 testsRock County: 49% of tests at or above 4 pCi/L · 4,112 testsRusk County: 37% of tests at or above 4 pCi/L · 363 testsSt. Croix County: 48% of tests at or above 4 pCi/L · 3,090 testsSauk County: 34% of tests at or above 4 pCi/L · 2,444 testsSawyer County: 32% of tests at or above 4 pCi/L · 649 testsShawano County: 49% of tests at or above 4 pCi/L · 884 testsSheboygan County: 42% of tests at or above 4 pCi/L · 2,896 testsTaylor County: 26% of tests at or above 4 pCi/L · 582 testsTrempealeau County: 42% of tests at or above 4 pCi/L · 950 testsVernon County: 55% of tests at or above 4 pCi/L · 1,434 testsVilas County: 31% of tests at or above 4 pCi/L · 1,315 testsWalworth County: 49% of tests at or above 4 pCi/L · 3,690 testsWashburn County: 35% of tests at or above 4 pCi/L · 438 testsWashington County: 46% of tests at or above 4 pCi/L · 5,615 testsWaukesha County: 46% of tests at or above 4 pCi/L · 23,315 testsWaupaca County: 52% of tests at or above 4 pCi/L · 1,447 testsWaushara County: 31% of tests at or above 4 pCi/L · 777 testsWinnebago County: 49% of tests at or above 4 pCi/L · 5,653 testsWood County: 34% of tests at or above 4 pCi/L · 1,966 tests
  • Under 10%
  • 10–20%
  • 20–30%
  • 30–40%
  • 40% or more
  • No data

About radon in Wisconsin

The Wisconsin Department of Health Services estimates that about 1 in 10 Wisconsin homes has high radon levels (Wisconsin DHS). Yet in the test records behind our county pages, 42% of results were at or above the EPA's 4 pCi/L action level. Both numbers can be right, and the gap is the most important thing to understand about Wisconsin's data.

Our figures come from 194,443 tests recorded in Wisconsin between 2005 and 2017. Those are homes whose owners chose to test, often because a neighbour found radon, a home was being sold, or the area is known for high levels. Tested homes are not a random sample, so the share of high tests runs well above the state's estimate for all homes. Use the county figures to compare places with each other, not as the odds for any single home.

Between counties, the differences are large. In our data, Langlade County in the north has the highest share of high results (59%) and Ashland County on Lake Superior the lowest (10%). The county map above shows the pattern.

Wisconsin takes a lighter regulatory approach than its neighbours. The state does not license radon testers or mitigators; DHS recommends hiring a professional certified by the National Radon Proficiency Program or the National Radon Safety Board (Wisconsin DHS). When a home is sold, the seller must tell the buyer about any known unsafe radon levels through the real estate condition report (Wisconsin DHS).

For local help, Wisconsin has 17 Radon Information Centers, each run by a health department serving several neighbouring counties (Wisconsin DHS). Pick your county below to see its results and how it compares with nearby counties.

Written and reviewed by Ray Roman · 2026-11-03

Counties

CountyTests% ≥ 4 pCi/LMedian (pCi/L)EPA zone (1993)Source
Adams County57318%1.6Zone 2Wisconsin county radon test results through 2017
Ashland County77010%1.1Zone 2Wisconsin county radon test results through 2017
Barron County1,15646%3.5Zone 2Wisconsin county radon test results through 2017
Bayfield County51424%2.0Zone 2Wisconsin county radon test results through 2017
Brown County5,29042%3.1Zone 2Wisconsin county radon test results through 2017
Buffalo County53251%4.0Zone 1Wisconsin county radon test results through 2017
Burnett County43023%2.3Zone 2Wisconsin county radon test results through 2017
Calumet County1,52947%3.5Zone 2Wisconsin county radon test results through 2017
Chippewa County2,20249%3.8Zone 2Wisconsin county radon test results through 2017
Clark County61029%2.3Zone 2Wisconsin county radon test results through 2017
Columbia County1,40535%2.5Zone 2Wisconsin county radon test results through 2017
Crawford County91154%4.5Zone 1Wisconsin county radon test results through 2017
Dane County18,79038%2.8Zone 1Wisconsin county radon test results through 2017
Dodge County2,20854%4.5Zone 1Wisconsin county radon test results through 2017
Door County2,55242%3.1Zone 1Wisconsin county radon test results through 2017
Douglas County63914%1.6Zone 2Wisconsin county radon test results through 2017
Dunn County1,39543%3.4Zone 2Wisconsin county radon test results through 2017
Eau Claire County3,51936%3.0Zone 2Wisconsin county radon test results through 2017
Florence County43539%3.2Zone 2Wisconsin county radon test results through 2017
Fond du Lac County2,91349%3.8Zone 1Wisconsin county radon test results through 2017
Forest County77037%2.8Zone 2Wisconsin county radon test results through 2017
Grant County2,37559%4.9Zone 1Wisconsin county radon test results through 2017
Green County1,13853%4.3Zone 1Wisconsin county radon test results through 2017
Green Lake County84746%3.6Zone 1Wisconsin county radon test results through 2017
Iowa County1,17255%4.5Zone 1Wisconsin county radon test results through 2017
Iron County28125%1.5Zone 2Wisconsin county radon test results through 2017
Jackson County52534%2.8Zone 2Wisconsin county radon test results through 2017
Jefferson County2,15739%2.9Zone 1Wisconsin county radon test results through 2017
Juneau County77416%1.4Zone 2Wisconsin county radon test results through 2017
Kenosha County5,79046%3.5Zone 2Wisconsin county radon test results through 2017
Kewaunee County43146%3.5Zone 2Wisconsin county radon test results through 2017
La Crosse County5,40836%2.9Zone 2Wisconsin county radon test results through 2017
Lafayette County52856%4.8Zone 1Wisconsin county radon test results through 2017
Langlade County1,24359%5.2Zone 1Wisconsin county radon test results through 2017
Lincoln County1,13737%2.9Zone 2Wisconsin county radon test results through 2017
Manitowoc County1,82432%2.4Zone 2Wisconsin county radon test results through 2017
Marathon County6,65957%5.0Zone 1Wisconsin county radon test results through 2017
Marinette County1,54024%1.8Zone 2Wisconsin county radon test results through 2017
Marquette County54013%1.3Zone 2Wisconsin county radon test results through 2017
Menominee County13035%2.9Zone 1Wisconsin county radon test results through 2017
Milwaukee County20,17033%2.3Zone 2Wisconsin county radon test results through 2017
Monroe County1,59123%1.9Zone 2Wisconsin county radon test results through 2017
Oconto County89443%3.4Zone 2Wisconsin county radon test results through 2017
Oneida County2,84829%2.4Zone 2Wisconsin county radon test results through 2017
Outagamie County5,78946%3.5Zone 2Wisconsin county radon test results through 2017
Ozaukee County4,40139%3.0Zone 2Wisconsin county radon test results through 2017
Pepin County32246%3.7Zone 1Wisconsin county radon test results through 2017
Pierce County1,52347%3.6Zone 1Wisconsin county radon test results through 2017
Polk County1,36938%3.0Zone 2Wisconsin county radon test results through 2017
Portage County2,25348%3.8Zone 1Wisconsin county radon test results through 2017
Price County84528%2.2Zone 2Wisconsin county radon test results through 2017
Racine County6,15146%3.5Zone 2Wisconsin county radon test results through 2017
Richland County1,02528%2.2Zone 1Wisconsin county radon test results through 2017
Rock County4,11249%3.9Zone 1Wisconsin county radon test results through 2017
Rusk County36337%2.8Zone 2Wisconsin county radon test results through 2017
Sauk County2,44434%2.5Zone 2Wisconsin county radon test results through 2017
Sawyer County64932%2.7Zone 2Wisconsin county radon test results through 2017
Shawano County88449%3.7Zone 1Wisconsin county radon test results through 2017
Sheboygan County2,89642%3.1Zone 2Wisconsin county radon test results through 2017
St. Croix County3,09048%3.8Zone 1Wisconsin county radon test results through 2017
Taylor County58226%1.9Zone 2Wisconsin county radon test results through 2017
Trempealeau County95042%3.3Zone 2Wisconsin county radon test results through 2017
Vernon County1,43455%4.4Zone 1Wisconsin county radon test results through 2017
Vilas County1,31531%2.6Zone 2Wisconsin county radon test results through 2017
Walworth County3,69049%3.7Zone 1Wisconsin county radon test results through 2017
Washburn County43835%2.8Zone 2Wisconsin county radon test results through 2017
Washington County5,61546%3.4Zone 1Wisconsin county radon test results through 2017
Waukesha County23,31546%3.5Zone 1Wisconsin county radon test results through 2017
Waupaca County1,44752%4.3Zone 1Wisconsin county radon test results through 2017
Waushara County77731%2.4Zone 2Wisconsin county radon test results through 2017
Winnebago County5,65349%3.9Zone 2Wisconsin county radon test results through 2017
Wood County1,96634%2.7Zone 1Wisconsin county radon test results through 2017

Test your home

County figures show how often tests come back high, not the level in your home. Only a test tells you that: see how to test for radon.

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