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Radon Levels in Dane County, Wisconsin

EPA puts Dane County in Zone 1, its highest radon zone, and 34.9% of its 2,887 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

    34.9%

    0.8 pts below WI

    Dane
    34.9%
    Wisconsin
    35.7%

    2,887 tests, 2023

  • Median result

    2.5pCi/L

    Below action level

    Dane
    2.5 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    2,887

    Most tested in Wisconsin

    Dane
    2,887

    Reported to CDC before any fix, 2023

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Wisconsin

    42 of 69

    Middle half

    Dane
    34.9%
    Langlade
    65.8%

    By share, of 69 with 30+ tests

Read a result for Dane County

Starts at Dane County's median, 2.5 pCi/L

2.5pCi/L

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

EPA’s reading of 2.5 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. Dane County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Dane County, At a glance

Dane County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Dane County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 72% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Dane County, 2023

Share of reported tests at or above 4 pCi/L, by year, Dane County
Share of reported tests at or above 4 pCi/L, by year, Dane County
YearShare of reported tests at or above 4 pCi/L
201449.6%
201550.7%
201648.8%
201744.5%
201940.7%
202036.7%
202135.2%
202237.5%
202334.9%

2023: 34.9%. Across these years the share ran from 34.9% to 50.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 2,887 tests reported to CDC for Dane 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

Dane County, Compared

Dane County radon figures, compared

Calculated by Radon411

In Dane County, about 3 in 10 reported tests in 2023 (1,009 of 2,887) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 1.5 points higher. Across 72 Wisconsin counties pooled together, 35.7% of tests reached that level, so Dane County runs 0.8 points below its state.

Of 7 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 2 a smaller one; the spread is 28.8% (Columbia County) to 61.0% (Iowa County). By share, Dane County is 42nd of 69 Wisconsin counties with 30 or more tests for the same period.

Year by year, 2014 opened at 49.6% and 2023 closed at 34.9% (down 14.7 points), with 2015 the high at 50.7%. Half the tests came in under 2.5 pCi/L and half over it; the single highest reached 60.4 pCi/L. Below the action level, 1,231 tests (42.6%) came in under 2 pCi/L, against 41.4% statewide, and 647 tests (22.4%) fell between 2 and 4, against 23.0% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 34.9% share point the same way here. USGS geology rates 72% of the county's land high radon potential. CDC also counts 123 tests taken after mitigation in Dane County for the same period: tests in homes where a fix was already in.

The busiest year on file was 2023, with 2,887 tests reported; the quietest, 2021, had 1,342.

Share of reported tests at or above 4 pCi/L by year, Dane County against Wisconsin2014 to 2023, years with 30 or more tests: Dane County 49.6% to 34.9%, the state's pooled share 35.7% in 2023.
Dane CountyWisconsin, pooled
Share of reported tests at or above 4 pCi/L by year, Dane County against Wisconsin: data table
YearTestsDane County, at or above 4 pCi/LWisconsin, pooled
20141,71149.6%51.1%
20151,82950.7%51.6%
20161,39748.8%45.2%
20171,42844.5%44.8%
20191,42540.7%42.9%
20201,53836.7%27.0%
20211,34235.2%39.9%
20221,76437.5%42.9%
20232,88734.9%35.7%
Dane County against Wisconsin, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Dane County
Dane County2,88734.9%2.5 pCi/LThis county
Wisconsin, pooled72 counties, pooled20,87935.7%Not pooled+0.8 points
United States, pooled642 counties, pooled128,74033.4%Not pooled−1.5 points
Langlade Countyhighest in the state22565.8%6.0 pCi/L+30.9 points
Bayfield Countylowest in the state355.7%1.5 pCi/L−29.2 points
Iowa County, WIborders it14661.0%4.8 pCi/L+26.1 points
Dodge County, WIborders it25754.9%4.8 pCi/L+20.0 points
Rock County, WIborders it45149.9%3.9 pCi/L+15.0 points
Jefferson County, WIborders it29644.3%3.5 pCi/L+9.4 points
Sauk County, WIborders it24141.1%3.3 pCi/L+6.2 points
Green County, WIborders it23533.6%2.1 pCi/L−1.3 points
Columbia County, WIborders it16328.8%2.0 pCi/L−6.1 points
Where Dane County's reported results fell, 2023, beside Wisconsin and the United States
ResultDane County testsDane County shareWisconsin shareU.S. shareAgainst Wisconsin
Under 2 pCi/L1,23142.6%41.4%41.4%+1.2 points
2 to 4 pCi/L64722.4%23.0%25.2%−0.6 points
4 pCi/L and above1,00934.9%35.7%33.4%−0.8 points
Dane 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
St. Croix County37 of 6934837.4%3.0 pCi/L
Racine County38 of 6944537.3%2.7 pCi/L
Price County39 of 696036.7%2.8 pCi/L
Chippewa County40 of 6931135.7%2.5 pCi/L
Portage County41 of 6933435.6%3.0 pCi/L
Dane County42 of 692,88734.9%2.5 pCi/L
Barron County43 of 6919934.7%2.5 pCi/L
Green County44 of 6923533.6%2.1 pCi/L
Polk County45 of 6912233.6%2.8 pCi/L
Richland County46 of 694833.3%2.9 pCi/L
Eau Claire County47 of 6947432.7%2.8 pCi/L
Dane County radon tests by year, against Wisconsin's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWisconsin, pooledChange from the row before
20232,88734.9%2.5 pCi/L60.4 pCi/L35.7%−2.6 points
20221,76437.5%2.7 pCi/L86.6 pCi/L42.9%+2.3 points
20211,34235.2%2.6 pCi/L96.8 pCi/L39.9%−1.5 points
20201,53836.7%2.9 pCi/L70.0 pCi/L27.0%−4.0 points
20191,42540.7%3.2 pCi/L111.3 pCi/L42.9%−3.8 points
20171,42844.5%3.5 pCi/L96.8 pCi/L44.8%−4.3 points
20161,39748.8%3.8 pCi/L105.3 pCi/L45.2%−1.9 points
20151,82950.7%4.0 pCi/L229.5 pCi/L51.6%+1.1 points
20141,71149.6%3.9 pCi/L103.1 pCi/L51.1%First on file

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

Dane County, Geology

The ground under Dane County

Predicted

USGS's geologic map splits Dane County: 72.0% of its land is high radon potential and 28.0% moderate. The map puts 51.6% of Dane County in the area it calls Eastern Ridges and Lowlands and 22.1% in Green Bay Lobe, with 2 smaller areas beside them. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).

USGS's geologic areas under Dane County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Eastern Ridges and LowlandsGlacial deposits derived from Ordovician carbonate rocks.High1251.6%
Green Bay LobeGlacial deposits derived from carbonate and igneous rocks.Moderate1022.1%
Driftless AreaCambrian sandstone and Ordovician limestone and dolostone.High1220.4%
Driftless AreaCambrian sandstone.Moderate105.9%

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

Dane County beside the ground around it

Dane County has more high-potential ground than Wisconsin as a whole: 72.0% of its land against 34.8%. Of the 7 counties that border it, 5 have more high-potential ground, Dodge County the most at 100%.

Share of land by USGS radon potential: Dane County, the 7 counties bordering it and Wisconsin
AreaEPA zoneLow potentialModerate potentialHigh potential
Dane CountyZone 1None28.0%72.0%
Green CountyZone 1NoneNone100%
Columbia CountyZone 2None64.1%35.9%
Rock CountyZone 1NoneNone100%
Jefferson CountyZone 1NoneNone100%
Iowa CountyZone 1None5.3%94.7%
Sauk CountyZone 2None99.9%0.1%
Dodge CountyZone 1NoneNone100%
Wisconsin72 counties, pooled by land areaVaries1.4%63.5%34.8%

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

Local help

Dane County, Local resources

Radon testing and mitigation in Dane 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

Dane County, Questions

Questions about radon in Dane County

Are radon levels high in Dane County?

In 2023, 34.9% of the radon tests reported to CDC for Dane County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.5 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 41 reported a higher share; pooled, the state comes to 35.7%.

Which counties border Dane County?

Dane County borders 7 counties: Green County, Columbia County, Rock County, Jefferson County, Iowa County, Sauk County and Dodge County.

Products

Dane County, Products

Testing a home in Dane County

In Dane County, 34.9% of 2,887 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Dane County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.

Test kits and monitors3

See every kit and monitor

Dane County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Dane County

Explore

Dane County, Bordering counties

Counties bordering Dane County

Calculated by Radon411

Dane County, Cities and towns

Cities and towns in Dane County

The Census Bureau estimates 590,375 residents in Dane County for July 1, 2025, 27,760 more than in 2020 (+4.9%). That works out to 493 people per square mile of land. Its largest town, Madison, has 286,233 residents, 48.5% of the total. CDC's 2,887 reported tests for 2023 work out to 4.9 per 1,000 residents (2025 estimate), close to Wisconsin's 3.5.

From Madison to Rockdale, CDC publishes no figure by town: each reads Dane County's.

The 12 largest cities and towns in Dane County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Madison286,233+4.1%48.5%
Sun Prairie39,227+8.9%6.6%
Fitchburg34,615+10.6%5.9%
Middleton23,115+4.7%3.9%
Verona16,821+20.3%2.8%
Waunakee16,411+10.0%2.8%
Stoughton13,256+0.7%2.2%
DeForest13,094+21.0%2.2%
Oregon12,015+6.9%2.0%
Windsor10,085+14.8%1.7%
McFarland9,145+1.1%1.5%
Cottage Grove8,930+20.9%1.5%
  • Monona
  • Mount Horeb
  • Edgerton (part)
  • Cross Plains
  • Marshall
  • Belleville (part)
  • Deerfield
  • Shorewood Hills
  • Mazomanie
  • Cambridge (part)
  • Brooklyn (part)
  • Black Earth
  • Maple Bluff
  • Dane
  • Blue Mounds
  • Rockdale

28 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).

Dane County, Homes

Homes in Dane County

Dane County has 254,880 homes, and many share a building: 33% are in buildings of five or more, 51% are detached houses, against 66% across Wisconsin. Much of Dane County is recent building: 30% of its homes have gone up since 2000 and the middle year built is 1985, against 1975 for Wisconsin. 58% 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 Dane County, Wisconsin, 2019 to 2023
HomesDane CountyWisconsin
Housing units254,8802,750,750
Detached houses51%66%
In buildings of 5 or more33%17%
Mobile homes1%3%
Built before 196021%34%
Built since 200030%20%
Middle year built19851975
Owner-occupied58%68%

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