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Radon Levels in Green Lake County, Wisconsin

EPA puts Green Lake County in Zone 1, its highest radon zone, and high results are common there: 40.5% of the 79 radon tests reported to CDC (2023) came back 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

    40.5%

    4.8 pts above WI

    Green Lake
    40.5%
    Wisconsin
    35.7%

    79 tests, 2023

  • Median result

    3.4pCi/L

    Below action level

    Green Lake
    3.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    79

    48th of 69 by tests

    Green Lake
    79
    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

    31 of 69

    Middle half

    Green Lake
    40.5%
    Langlade
    65.8%

    By share, of 69 with 30+ tests

Read a result for Green Lake County

Starts at Green Lake County's median, 3.4 pCi/L

3.4pCi/L

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

EPA’s reading of 3.4 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. Green Lake County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Green Lake County, At a glance

Green Lake County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Green Lake 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: Moderate across 58% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Green Lake County, 2023

Share of reported tests at or above 4 pCi/L, by year, Green Lake County
Share of reported tests at or above 4 pCi/L, by year, Green Lake County
YearShare of reported tests at or above 4 pCi/L
201449.3%
201540.5%
201644.4%
201742.1%
201939.8%
202039.5%
202139.6%
202242.1%
202340.5%

2023: 40.5%. Across these years the share ran from 39.5% to 49.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 79 tests reported to CDC for Green Lake 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

Green Lake County, Compared

Green Lake County radon figures, compared

Calculated by Radon411

In Green Lake County, about 4 in 10 reported tests in 2023 (32 of 79) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 7.1 points higher. Across 72 Wisconsin counties pooled together, 35.7% of tests reached that level, so Green Lake County runs 4.8 points above its state.

Of 6 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 15.0% (Marquette County) to 54.9% (Dodge County). By share, Green Lake County is 31st of 69 Wisconsin counties with 30 or more tests for the same period.

Year by year, 2014 opened at 49.3% and 2023 closed at 40.5% (down 8.8 points), with 2014 the high at 49.3%. Half the tests came in under 3.4 pCi/L and half over it; the single highest reached 151.8 pCi/L. Below the action level, 28 tests (35.4%) came in under 2 pCi/L, against 41.4% statewide, and 19 tests (24.1%) fell between 2 and 4, against 23.0% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 40.5% share point the same way here. USGS geology rates 58% of the county's land moderate radon potential.

The busiest year on file was 2016, with 126 tests reported; the quietest, 2021, had 53.

Share of reported tests at or above 4 pCi/L by year, Green Lake County against Wisconsin2014 to 2023, years with 30 or more tests: Green Lake County 49.3% to 40.5%, the state's pooled share 35.7% in 2023.
Green Lake CountyWisconsin, pooled
Share of reported tests at or above 4 pCi/L by year, Green Lake County against Wisconsin: data table
YearTestsGreen Lake County, at or above 4 pCi/LWisconsin, pooled
20147349.3%51.1%
20158440.5%51.6%
201612644.4%45.2%
201711442.1%44.8%
20199839.8%42.9%
202012439.5%27.0%
20215339.6%39.9%
20227642.1%42.9%
20237940.5%35.7%
Green Lake County against Wisconsin, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Green Lake County
Green Lake County7940.5%3.4 pCi/LThis county
Wisconsin, pooled72 counties, pooled20,87935.7%Not pooled−4.8 points
United States, pooled642 counties, pooled128,74033.4%Not pooled−7.1 points
Langlade Countyhighest in the state22565.8%6.0 pCi/L+25.3 points
Bayfield Countylowest in the state355.7%1.5 pCi/L−34.8 points
Dodge County, WIborders it25754.9%4.8 pCi/L+14.4 points
Winnebago County, WIborders it51242.4%3.1 pCi/L+1.9 points
Columbia County, WIborders it16328.8%2.0 pCi/L−11.7 points
Waushara County, WIborders it7125.4%1.9 pCi/L−15.1 points
Fond du Lac County, WIborders it98419.6%1.4 pCi/L−20.9 points
Marquette County, WIborders it4015.0%1.3 pCi/L−25.5 points
Where Green Lake County's reported results fell, 2023, beside Wisconsin and the United States
ResultGreen Lake County testsGreen Lake County shareWisconsin shareU.S. shareAgainst Wisconsin
Under 2 pCi/L2835.4%41.4%41.4%−6.0 points
2 to 4 pCi/L1924.1%23.0%25.2%+1.1 points
4 pCi/L and above3240.5%35.7%33.4%+4.8 points
Green Lake 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
Door County26 of 6915642.3%3.0 pCi/L
Trempealeau County27 of 6911242.0%3.3 pCi/L
Sauk County28 of 6924141.1%3.3 pCi/L
Oneida County29 of 6913540.7%2.7 pCi/L
Outagamie County30 of 6933740.7%3.1 pCi/L
Green Lake County31 of 697940.5%3.4 pCi/L
Forest County32 of 694540.0%2.9 pCi/L
Jackson County33 of 699338.7%3.2 pCi/L
Rusk County34 of 695738.6%3.2 pCi/L
Walworth County35 of 6934037.9%2.8 pCi/L
Dunn County36 of 6917137.4%2.9 pCi/L
Green Lake County radon tests by year, against Wisconsin's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWisconsin, pooledChange from the row before
20237940.5%3.4 pCi/L151.8 pCi/L35.7%−1.6 points
20227642.1%3.0 pCi/L23.1 pCi/L42.9%+2.5 points
20215339.6%3.1 pCi/L159.5 pCi/L39.9%+0.1 points
202012439.5%2.9 pCi/L143.7 pCi/L27.0%−0.3 points
20199839.8%3.1 pCi/L113.7 pCi/L42.9%−2.3 points
201711442.1%3.0 pCi/L42.6 pCi/L44.8%−2.3 points
201612644.4%3.3 pCi/L47.4 pCi/L45.2%+3.9 points
20158440.5%3.5 pCi/L46.7 pCi/L51.6%−8.8 points
20147349.3%3.8 pCi/L89.3 pCi/L51.1%First on file

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

Green Lake County, Geology

The ground under Green Lake County

Predicted

USGS's geologic map splits Green Lake County: 57.5% of its land is moderate radon potential and 42.5% high. The map puts 57.5% of Green Lake County in the area it calls Green Bay Lobe and 42.5% in Eastern Ridges and Lowlands. 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 Green Lake County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Green Bay LobeGlacial deposits derived from carbonate and igneous rocks.Moderate1057.5%
Eastern Ridges and LowlandsGlacial deposits derived from Ordovician carbonate rocks.High1242.5%

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

Green Lake County beside the ground around it

On high-potential ground Green Lake County is close to Wisconsin as a whole: 42.5% of its land against 34.8%. Of the 6 counties that border it, 2 have more high-potential ground, Dodge County the most at 100%.

Share of land by USGS radon potential: Green Lake County, the 6 counties bordering it and Wisconsin
AreaEPA zoneLow potentialModerate potentialHigh potential
Green Lake CountyZone 1None57.5%42.5%
Marquette CountyZone 2None100%None
Waushara CountyZone 2None100%None
Fond du Lac CountyZone 1None10.6%89.4%
Columbia CountyZone 2None64.1%35.9%
Dodge CountyZone 1NoneNone100%
Winnebago CountyZone 2None81.5%18.5%
Wisconsin72 counties, pooled by land areaVaries1.4%63.5%34.8%

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

Local help

Green Lake County, Local resources

Radon testing and mitigation in Green Lake 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

Green Lake County, Questions

Questions about radon in Green Lake County

Are radon levels high in Green Lake County?

In 2023, 40.5% of the radon tests reported to CDC for Green Lake County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.4 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 30 reported a higher share; pooled, the state comes to 35.7%.

Which counties border Green Lake County?

Green Lake County borders 6 counties: Marquette County, Waushara County, Fond du Lac County, Columbia County, Dodge County and Winnebago County.

Products

Green Lake County, Products

Testing a home in Green Lake County

In Green Lake County, 40.5% of 79 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Green Lake 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

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

Explore

Green Lake County, Bordering counties

Counties bordering Green Lake County

Calculated by Radon411

Green Lake County, Cities and towns

Cities and towns in Green Lake County

The Census Bureau estimates 19,305 residents in Green Lake County for July 1, 2025, 289 more than in 2020 (+1.5%). That works out to 55 people per square mile of land. Berlin, the largest place on its list (5,588 residents in all), extends beyond Green Lake County, so no share of the total is worked out for it. CDC's 79 reported tests for 2023 work out to 4.1 per 1,000 residents (2025 estimate), close to Wisconsin's 3.5.

From Berlin to Marquette, CDC publishes no figure by town: each reads Green Lake County's.

The cities and towns in Green Lake County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Berlinextends beyond Green Lake County5,588+0.2%Counted whole
Markesan1,380−0.1%7.1%
Princeton1,249−0.6%6.5%
Green Lake1,040+2.4%5.4%
Kingston289−0.3%1.5%
Marquette173+0.6%0.9%

6 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 Green Lake County is counted whole, so it has no share.

Green Lake County, Homes

Homes in Green Lake County

Green Lake County is a place of houses on their own lots: 81% of its 10,731 homes are detached single-family houses, against 66% across Wisconsin. Half of its homes were built before 1971, close to Wisconsin's 1975: 39% date from before 1960 and 14% from 2000 or later. Owners live in 75% of the occupied homes (Wisconsin: 68%), so for most households a test and a fix are their own to order.

Homes in Green Lake County, Wisconsin, 2019 to 2023
HomesGreen Lake CountyWisconsin
Housing units10,7312,750,750
Detached houses81%66%
In buildings of 5 or more9%17%
Mobile homes4%3%
Built before 196039%34%
Built since 200014%20%
Middle year built19711975
Owner-occupied75%68%

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