EPA radon zones in Wisconsin
The EPA sorts counties into zones by the radon level predicted for an average indoor screening measurement. This page labels the data "EPA radon zones (1993 map)" so the date stays visible. Wisconsin has two zones in use.[1]
- Zone 1 (highest potential): 28 counties with a predicted average indoor screening level greater than 4 pCi/L.
- Zone 2 (moderate potential): 44 counties with a predicted average of 2 to 4 pCi/L.
- Zone 3: no Wisconsin county.
Some third-party pages say Wisconsin as a whole is "Zone 1." That is loose wording.
The EPA assigns zones county by county, and 44 of the state's counties are Zone 2.[1]
Side by side
Wisconsin radon zones compared
Zone 1
- 28 counties
- Predicted average above 4 pCi/L
Zone 2
- 44 counties
- Predicted average 2 to 4 pCi/L
The EPA says the map draws on indoor radon measurements, geology, aerial radioactivity, soil characteristics and foundation types.[6] It is a regional prediction, not a house-by-house reading.
Wisconsin counties in Zone 1 and Zone 2
Find your county below. Both lists come from the EPA's Wisconsin map, labelled EPA radon zones (1993 map).[1][2]
| Zone | Counties |
|---|---|
| Zone 1 (28 counties, predicted average above 4 pCi/L) | Buffalo, Crawford, Dane, Dodge, Door, Fond du Lac, Grant, Green, Green Lake, Iowa, Jefferson, Lafayette, Langlade, Marathon, Menominee, Pepin, Pierce, Portage, Richland, Rock, Shawano, St. Croix, Vernon, Walworth, Washington, Waukesha, Waupaca, Wood |
| Zone 2 (44 counties, predicted average 2 to 4 pCi/L) | Adams, Ashland, Barron, Bayfield, Brown, Burnett, Calumet, Chippewa, Clark, Columbia, Douglas, Dunn, Eau Claire, Florence, Forest, Iron, Jackson, Juneau, Kenosha, Kewaunee, La Crosse, Lincoln, Manitowoc, Marinette, Marquette, Milwaukee, Monroe, Oconto, Oneida, Outagamie, Ozaukee, Polk, Price, Racine, Rusk, Sauk, Sawyer, Sheboygan, Taylor, Trempealeau, Vilas, Washburn, Waushara, Winnebago |
Counties on either side of a zone line can look very alike in real homes.
A county's zone is a label for an average, so treat it as a starting point and not a verdict.
Why every home should be tested, whatever the map says
The EPA is blunt about it: "All homes should be tested, regardless of zone designation."[1] The same message is repeated in its supplemental guidance on the map.[6]
The logic is simple. A zone is a county-wide prediction, and one house can differ from the next house down the street.
A Zone 2 label does not make a basement safe, and a Zone 1 label does not mean your house is high.
Which map answers which question
You will run into more than one map, and they answer different questions.
| Map | What it is | What it can tell you |
|---|---|---|
| EPA radon zones (1993 map) | County-level prediction by zone | Whether radon is more or less likely in your county[1] |
| DHS interactive radon map | Wisconsin Department of Health Services map of published test results | What tests in your area have found[5] |
| Commercial city-level maps | Third-party estimates | A rough idea only, not a measurement of your house |
The state health department (DHS) publishes its test results as an interactive map, and it says the map should not be used to judge any one home.[3][4]
Use it to see the local picture, then measure your own house.
Interpreting a radon test result in pCi/L
Radon is measured in picocuries per liter (pCi/L). The EPA recommends fixing a home at 4 pCi/L or higher and considering it between 2 and 4 pCi/L.[1][7]
| Result | What the EPA guidance says |
|---|---|
| Below 2 pCi/L | Under the range where the EPA suggests considering a fix |
| 2 to 4 pCi/L | Consider fixing[1] |
| 4 pCi/L or higher | EPA recommends fixing[1] |
Where you place the test matters. Wisconsin Extension guidance recommends testing the lowest livable level of the home, which for many houses is the basement.[7]
Follow the kit's directions on keeping windows and doors closed, since ventilation can distort a reading.[6]
If a first result lands near 4 pCi/L, repeat it before deciding. Ask the county health department or the DHS radon program whether low-cost kits are available where you live, and check what a kit costs before you order.
Step by step
From map to test result
Find your county
Look it up in the zone table above.
Place a test kit
Put it on the lowest livable level.
Read the result
Compare it with the 2 and 4 pCi/L marks.
Retest or call a pro
Confirm the result, or call a qualified professional.
A simple order of steps
- Find your county in the table above.
- Order a test kit and place it on the lowest livable level.
- Read the result against the 2 and 4 pCi/L marks.
- Retest to confirm, or call a qualified professional.
Hiring a certified professional for high radon levels
Wisconsin Extension guidance advises that when results are elevated, you consider hiring a certified radon mitigation professional.[7] This page does not set out how a system is designed or what it costs, because no cited source here supports those details.
Ask each installer to explain their plan in plain terms.
When you compare quotes, ask where the suction points go, how the pipe is routed, where the fan sits, what the warranty covers and how the system will be tested afterward. A house with more than one foundation section, such as an addition, may need a different design from a simple basement, so ask whether the plan accounts for that.
After any work, retest. Ask the installer what you should monitor going forward.
If the basement is also damp, the two problems can overlap in the same room, and the wet basements guide is a good starting point. Ask your city's permit desk which rules apply. For a pro who works on basements, see Badger Basements.
The state DHS radon program and the EPA have the final word on testing and fixing guidance. For permits tied to any work in your home, check with your city or building inspector.[3]
Zone data checked 2026 against the EPA's Wisconsin map.
Sources
- U.S. Environmental Protection Agency. "Wisconsin: EPA Map of Radon Zones (1993 map)." https://www.epa.gov/sites/default/files/2014-08/documents/wisconsin.pdf. Accessed October 17, 2026.
- U.S. Environmental Protection Agency. "EPA Map of Radon Zones." https://www.epa.gov/radon/epa-map-radon-zones. Accessed October 17, 2026.
- Wisconsin Department of Health Services. "Radon in Wisconsin (DHS)." https://www.dhs.wisconsin.gov/radon/index.htm. Accessed October 17, 2026.
- Wisconsin Department of Health Services. "Radon in Wisconsin (DHS)." https://www.dhs.wisconsin.gov/radon/radon-results.htm. Accessed October 17, 2026.
- Wisconsin Department of Health Services. "Radon in Wisconsin (DHS)." https://dhsgis.wi.gov/dhs/radon/. Accessed October 17, 2026.
- U.S. Environmental Protection Agency. "EPA Map of Radon Zones and Supplemental Information." https://www.epa.gov/radon/epa-map-radon-zones-and-supplemental-information. Accessed October 17, 2026.
- University of Wisconsin–Madison Division of Extension, Fond du Lac County. "Radon Testing at Home." https://fonddulac.extension.wisc.edu/homeradontesting/. Accessed October 17, 2026.