Radon in Wisconsin: radon map by county

EPA's Map of Radon Zones puts 28 of Wisconsin's 72 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 44 in Zone 2 and 0 in Zone 3. Of 55,359 building tests that radon laboratories reported for 2008 to 2017, 47% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 6 of 42 states with 1,000+ tests). The highest county share is Langlade County (68% of 166 tests).

counties in Zone 1 (above 4 pCi/L predicted)

counties in Zone 2 (2 to 4)

counties in Zone 3 (below 2)

47%

of 55,359 lab tests at or above 4 pCi/L

Radon by county in Wisconsin

EPA radon zone and radon test results for each county in Wisconsin
County	EPA zone	Lab tests	Median	4+ pCi/L
Adams County	Zone 2	92	2.2	21.2%
Ashland County	Zone 2	175	1.5	12.8%
Barron County	Zone 2	307	3.5	42.9%
Bayfield County	Zone 2	193	2.6	32.2%
Brown County	Zone 2	1,643	4.1	51.5%
Buffalo County	Zone 1	82	3.6	41.8%
Burnett County	Zone 2	103	2.9	33.1%
Calumet County	Zone 2	334	4.7	59.8%
Chippewa County	Zone 2	676	4.6	55.9%
Clark County	Zone 2	95	3.6	43.6%
Columbia County	Zone 2	317	2.8	38.6%
Crawford County	Zone 1	138	5.1	59.4%
Dane County	Zone 1	5,024	2.8	39.4%
Dodge County	Zone 1	815	5.6	63.3%
Door County	Zone 1	431	2.9	41%
Douglas County	Zone 2	200	2.0	24.2%
Dunn County	Zone 2	285	4.0	50.8%
Eau Claire County	Zone 2	1,035	3.1	39.5%
Florence County	Zone 2	103	4.3	52.1%
Fond du Lac County	Zone 1	970	4.6	56.4%
Forest County	Zone 2	62	4.2	55.6%
Grant County	Zone 1	478	5.5	64%
Green County	Zone 1	262	4.3	51.7%
Green Lake County	Zone 1	124	4.5	53.6%
Iowa County	Zone 1	322	5.4	63.2%
Iron County	Zone 2	32	2.0	28.6%
Jackson County	Zone 2	100	3.3	44%
Jefferson County	Zone 1	956	3.8	48.6%
Juneau County	Zone 2	82	2.5	26.7%
Kenosha County	Zone 2	1,440	3.0	41.3%
Kewaunee County	Zone 2	137	4.1	51.2%
La Crosse County	Zone 2	1,973	3.1	37.7%
Lafayette County	Zone 1	98	5.4	61.9%
Langlade County	Zone 1	166	7.4	68%
Lincoln County	Zone 2	263	3.8	46.2%
Manitowoc County	Zone 2	691	3.2	40.2%
Marathon County	Zone 1	2,008	4.4	53.3%
Marinette County	Zone 2	312	2.2	27.9%
Marquette County	Zone 2	110	1.3	14.2%
Menominee County	Zone 1	1	10.3	100%
Milwaukee County	Zone 2	6,266	3.2	42.7%
Monroe County	Zone 2	480	2.4	30.1%
Oconto County	Zone 2	250	3.9	49.7%
Oneida County	Zone 2	671	2.9	36.8%
Outagamie County	Zone 2	1,237	4.5	55.9%
Ozaukee County	Zone 2	1,308	3.6	46.4%
Pepin County	Zone 1	98	3.8	49.1%
Pierce County	Zone 1	426	3.7	47.9%
Polk County	Zone 2	501	2.9	35.6%
Portage County	Zone 1	496	4.6	56.5%
Price County	Zone 2	192	3.0	42.9%
Racine County	Zone 2	2,384	3.9	49.2%
Richland County	Zone 1	128	2.7	35.3%
Rock County	Zone 1	1,467	4.2	52.9%
Rusk County	Zone 2	234	3.1	41.4%
Sauk County	Zone 2	614	2.8	37.3%
Sawyer County	Zone 2	76	2.4	25.6%
Shawano County	Zone 1	121	4.4	52.3%
Sheboygan County	Zone 2	557	2.9	41.5%
St. Croix County	Zone 1	1,481	3.6	45.9%
Taylor County	Zone 2	73	2.5	34.8%
Trempealeau County	Zone 2	245	3.8	48.7%
Vernon County	Zone 1	332	5.4	60.7%
Vilas County	Zone 2	349	2.9	35.7%
Walworth County	Zone 1	1,057	4.3	52.5%
Washburn County	Zone 2	95	2.7	31.6%
Washington County	Zone 1	2,349	4.7	56%
Waukesha County	Zone 1	5,885	4.1	51.4%
Waupaca County	Zone 1	602	5.4	62.7%
Waushara County	Zone 2	166	2.8	35.8%
Winnebago County	Zone 2	1,737	4.6	56.4%
Wood County	Zone 1	847	3.2	37.7%

Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).

What the zones mean

Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.

Radon in Wisconsin: questions

What radon zone is Wisconsin?

EPA's 1993 map does not give states one zone; it zones each county. In Wisconsin, 28 counties are Zone 1, 44 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".

Which Wisconsin counties have the highest radon levels?

By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Langlade County 68% (median 7.4 pCi/L, 166 tests); Grant County 64% (median 5.5 pCi/L, 478 tests); Dodge County 63.3% (median 5.6 pCi/L, 815 tests); Iowa County 63.2% (median 5.4 pCi/L, 322 tests); Waupaca County 62.7% (median 5.4 pCi/L, 602 tests).

How common is high radon in Wisconsin?

47% of the 55,359 tests in the laboratory data for Wisconsin (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.

Does Wisconsin publish its own radon test data?

Wisconsin's radon program reports county test results; the latest year with county results is 2023, shown on each county page.

Should I test for radon in Wisconsin?

Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.

States bordering Wisconsin

Radon in Illinois (56 of 102 in Zone 1)Radon in Iowa (99 of 99 in Zone 1)Radon in Michigan (9 of 83 in Zone 1)Radon in Minnesota (68 of 87 in Zone 1)

Other free hazard lookups

All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).

Superfund sites in Wisconsin · Radon map of every state

Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.