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Radon Levels in Monroe County, Wisconsin

EPA puts Monroe County in Zone 2, its middle radon zone, and 22.5% of its 213 reported radon tests (2023) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    22.5%

    13.2 pts below WI

    Monroe
    22.5%
    Wisconsin
    35.7%

    213 tests, 2023

  • Median result

    2.2pCi/L

    Below action level

    Monroe
    2.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    213

    28th of 69 by tests

    Monroe
    213
    Dane
    2,887

    Reported to CDC before any fix, 2023

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Wisconsin

    58 of 69

    Lowest quarter

    Monroe
    22.5%
    Langlade
    65.8%

    By share, of 69 with 30+ tests

Read a result for Monroe County

Starts at Monroe County's median, 2.2 pCi/L

2.2pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 2.2 pCi/L

Between 2 and 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Monroe County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Monroe County, At a glance

Monroe County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Monroe County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 91% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Monroe County, 2023

Share of reported tests at or above 4 pCi/L, by year, Monroe County
Share of reported tests at or above 4 pCi/L, by year, Monroe County
YearShare of reported tests at or above 4 pCi/L
201446.8%
201541.7%
201634.8%
201728.3%
201926.8%
202015.5%
202124.5%
202223.3%
202322.5%

2023: 22.5%. Across these years the share ran from 15.5% to 46.8%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 213 tests reported to CDC for Monroe County over 2023, many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Monroe County, Compared

Monroe County radon figures, compared

Calculated by Radon411

Monroe County's 213 reported tests in 2023 had a middle value of 2.2 pCi/L and a maximum of 24.4 pCi/L, and 22.5% reached 4 pCi/L. Wisconsin as a whole (72 Wisconsin counties, pooled) comes to 35.7%: 13.2 points higher than here.

Among its state's counties it ranks 58th of 69 Wisconsin counties with 30 or more tests for the same period. Statewide for the same period, Langlade County reported the highest share (65.8%) and Bayfield County the lowest (5.7%).

Below the action level, 103 tests (48.4%) came in under 2 pCi/L, against 41.4% statewide, and 62 tests (29.1%) fell between 2 and 4, against 23.0% statewide. The busiest year on file was 2023, with 213 tests reported; the quietest, 2014, had 47.

EPA's 1993 zone map puts Monroe County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 91% of the county's land moderate radon potential.

Next door, the shares run from 10.0% in Juneau County to 47.5% in Vernon County, with Juneau County below Monroe County. Over 9 years of annual figures the share fell 24.3 points, from 46.8% in 2014 to 22.5% in 2023; its peak was 46.8% in 2014.

CDC also counts 5 tests taken after mitigation in Monroe County for the same period: tests in homes where a fix was already in.

Share of reported tests at or above 4 pCi/L by year, Monroe County against Wisconsin2014 to 2023, years with 30 or more tests: Monroe County 46.8% to 22.5%, the state's pooled share 35.7% in 2023.
Monroe CountyWisconsin, pooled
Share of reported tests at or above 4 pCi/L by year, Monroe County against Wisconsin: data table
YearTestsMonroe County, at or above 4 pCi/LWisconsin, pooled
20144746.8%51.1%
201512741.7%51.6%
201615834.8%45.2%
201715928.3%44.8%
201920526.8%42.9%
202019315.5%27.0%
202110624.5%39.9%
202213323.3%42.9%
202321322.5%35.7%
Monroe County against Wisconsin, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Monroe County
Monroe County21322.5%2.2 pCi/LThis county
Wisconsin, pooled72 counties, pooled20,87935.7%Not pooled+13.2 points
United States, pooled642 counties, pooled128,74033.4%Not pooled+10.9 points
Langlade Countyhighest in the state22565.8%6.0 pCi/L+43.3 points
Bayfield Countylowest in the state355.7%1.5 pCi/L−16.8 points
Vernon County, WIborders it16247.5%3.8 pCi/L+25.0 points
Jackson County, WIborders it9338.7%3.2 pCi/L+16.2 points
La Crosse County, WIborders it77131.4%2.7 pCi/L+8.9 points
Juneau County, WIborders it5010.0%1.1 pCi/L−12.5 points
Where Monroe County's reported results fell, 2023, beside Wisconsin and the United States
ResultMonroe County testsMonroe County shareWisconsin shareU.S. shareAgainst Wisconsin
Under 2 pCi/L10348.4%41.4%41.4%+7.0 points
2 to 4 pCi/L6229.1%23.0%25.2%+6.1 points
4 pCi/L and above4822.5%35.7%33.4%−13.2 points
Monroe County ranked among the 69 Wisconsin counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
Waushara County53 of 697125.4%1.9 pCi/L
Clark County54 of 697525.3%2.2 pCi/L
Lincoln County55 of 698123.5%2.1 pCi/L
Burnett County56 of 695223.1%1.6 pCi/L
Brown County57 of 6955123.0%1.4 pCi/L
Monroe County58 of 6921322.5%2.2 pCi/L
Vilas County59 of 6910621.7%2.1 pCi/L
Adams County60 of 694820.8%1.7 pCi/L
Milwaukee County61 of 692,60520.2%1.5 pCi/L
Fond du Lac County62 of 6998419.6%1.4 pCi/L
Taylor County63 of 693718.9%2.1 pCi/L
Monroe County radon tests by year, against Wisconsin's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWisconsin, pooledChange from the row before
202321322.5%2.2 pCi/L24.4 pCi/L35.7%−0.8 points
202213323.3%2.0 pCi/L23.8 pCi/L42.9%−1.2 points
202110624.5%2.5 pCi/L13.1 pCi/L39.9%+9.0 points
202019315.5%1.3 pCi/L60.6 pCi/L27.0%−11.3 points
201920526.8%2.2 pCi/L31.4 pCi/L42.9%−1.5 points
201715928.3%2.1 pCi/L42.6 pCi/L44.8%−6.5 points
201615834.8%2.3 pCi/L40.9 pCi/L45.2%−6.9 points
201512741.7%3.3 pCi/L67.4 pCi/L51.6%−5.1 points
20144746.8%3.7 pCi/L47.6 pCi/L51.1%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Monroe County, Geology

The ground under Monroe County

Predicted

Most of the ground under Monroe County is one class on USGS's geologic map: 91.2% of its land is moderate radon potential, with 8.8% high. The map puts 91.2% of Monroe County in the area it calls Driftless Area and 8.8% in Driftless Area. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 12, in the high band (12 to 17).

USGS's geologic areas under Monroe County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Driftless AreaCambrian sandstone.Moderate1091.2%
Driftless AreaCambrian sandstone and Ordovician limestone and dolostone.High128.8%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Monroe County beside the ground around it

Wisconsin as a whole has more high-potential ground than Monroe County: 34.8% of its land, against 8.8% here. Of the 4 counties that border it, 2 have more high-potential ground, Vernon County the most at 83.1%.

Share of land by USGS radon potential: Monroe County, the 4 counties bordering it and Wisconsin
AreaEPA zoneLow potentialModerate potentialHigh potential
Monroe CountyZone 2None91.2%8.8%
Juneau CountyZone 2None100%None
Vernon CountyZone 1None16.9%83.1%
La Crosse CountyZone 2None66.4%33.6%
Jackson CountyZone 2None100%None
Wisconsin72 counties, pooled by land areaVaries1.4%63.5%34.8%

The map rates the ground, not the air in any home.

Local help

Monroe County, Local resources

Radon testing and mitigation in Monroe County

What Wisconsin's program says
Phone
1-888-569-7236
Email
DHSRadon@dhs.wisconsin.gov
Licensing of radon professionals
The State of Wisconsin does not require contractors performing radon measurement or mitigation work to be state licensed or nationally certified.

What it means

Monroe County, Questions

Questions about radon in Monroe County

Are radon levels high in Monroe County?

In 2023, 22.5% of the radon tests reported to CDC for Monroe County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.2 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 57 reported a higher share; pooled, the state comes to 35.7%.

Which counties border Monroe County?

Monroe County borders 4 counties: Juneau County, Vernon County, La Crosse County and Jackson County.

Products

Monroe County, Products

Testing a home in Monroe County

In Monroe County, 22.5% of 213 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Monroe County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Monroe County homes, compared

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Monroe County, Bordering counties

Counties bordering Monroe County

Calculated by Radon411

Monroe County, Cities and towns

Cities and towns in Monroe County

The Census Bureau estimates 46,572 residents in Monroe County for July 1, 2025, 265 more than in 2020 (+0.6%). That works out to 52 people per square mile of land. Its largest town, Sparta, has 9,974 residents, 21.4% of the total. CDC's 213 reported tests for 2023 work out to 4.6 per 1,000 residents (2025 estimate), close to Wisconsin's 3.5.

From Sparta to Melvina, CDC publishes no figure by town: each reads Monroe County's.

The cities and towns in Monroe County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Sparta9,974−0.6%21.4%
Tomah9,600+0.4%20.6%
Cashton1,174+1.2%2.5%
Rocklandextends beyond Monroe County754−2.0%Counted whole
Norwalk604−1.0%1.3%
Warrens534−0.2%1.1%
Ontarioextends beyond Monroe County528−0.8%Counted whole
Wilton523−1.7%1.1%
Kendall465−2.5%1.0%
Oakdale307+2.0%0.7%
Wyeville117−4.1%0.3%
Melvina94+2.2%0.2%

12 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Monroe County is counted whole, so it has no share.

Monroe County, Homes

Homes in Monroe County

Of Monroe County's 19,918 homes, 73% are detached houses, against 66% across Wisconsin; 8% are in buildings of five or more homes. Half of its homes were built before 1980, close to Wisconsin's 1975: 31% date from before 1960 and 23% from 2000 or later. 72% of occupied homes are lived in by their owner (Wisconsin: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Monroe County, Wisconsin, 2019 to 2023
HomesMonroe CountyWisconsin
Housing units19,9182,750,750
Detached houses73%66%
In buildings of 5 or more8%17%
Mobile homes8%3%
Built before 196031%34%
Built since 200023%20%
Middle year built19801975
Owner-occupied72%68%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.