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Radon Levels in Fond du Lac County, Wisconsin

EPA puts Fond du Lac County in Zone 1, its highest radon zone, and 19.6% of its 984 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

    19.6%

    16.1 pts below WI

    Fond du Lac
    19.6%
    Wisconsin
    35.7%

    984 tests, 2023

  • Median result

    1.4pCi/L

    Below action level

    Fond du Lac
    1.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    984

    4th of 69 by tests

    Fond du Lac
    984
    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

    62 of 69

    Lowest quarter

    Fond du Lac
    19.6%
    Langlade
    65.8%

    By share, of 69 with 30+ tests

Read a result for Fond du Lac County

Starts at Fond du Lac County's median, 1.4 pCi/L

1.4pCi/L

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

EPA’s reading of 1.4 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Fond du Lac County's median reported result, 2023.

Interpret this reading

The data

Fond du Lac County, At a glance

Fond du Lac County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Fond du Lac 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 89% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Fond du Lac County, 2023

Share of reported tests at or above 4 pCi/L, by year, Fond du Lac County
Share of reported tests at or above 4 pCi/L, by year, Fond du Lac County
YearShare of reported tests at or above 4 pCi/L
201456.3%
201552.1%
201653.5%
201750.0%
201950.2%
202045.3%
202141.7%
202255.1%
202319.6%

2023: 19.6%. Across these years the share ran from 19.6% to 56.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 984 tests reported to CDC for Fond du Lac 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

Fond du Lac County, Compared

Fond du Lac County radon figures, compared

Calculated by Radon411

Fond du Lac County's 984 reported tests in 2023 had a middle value of 1.4 pCi/L and a maximum of 43.4 pCi/L, and 19.6% reached 4 pCi/L. Wisconsin as a whole (72 Wisconsin counties, pooled) comes to 35.7%: 16.1 points higher than here.

Among its state's counties it ranks 62nd 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, 612 tests (62.2%) came in under 2 pCi/L, against 41.4% statewide, and 179 tests (18.2%) fell between 2 and 4, against 23.0% statewide. The busiest year on file was 2023, with 984 tests reported; the quietest, 2017, had 170.

EPA's 1993 zone map puts Fond du Lac County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 89% of the county's land high radon potential.

Next door, the shares run from 40.5% in Green Lake County to 54.9% in Dodge County. Over 9 years of annual figures the share fell 36.7 points, from 56.3% in 2014 to 19.6% in 2023; its peak was 56.3% in 2014.

CDC also counts 31 tests taken after mitigation in Fond du Lac 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, Fond du Lac County against Wisconsin2014 to 2023, years with 30 or more tests: Fond du Lac County 56.3% to 19.6%, the state's pooled share 35.7% in 2023.
Fond du Lac CountyWisconsin, pooled
Share of reported tests at or above 4 pCi/L by year, Fond du Lac County against Wisconsin: data table
YearTestsFond du Lac County, at or above 4 pCi/LWisconsin, pooled
201437356.3%51.1%
201533852.1%51.6%
201631453.5%45.2%
201717050.0%44.8%
201925750.2%42.9%
202023245.3%27.0%
202126441.7%39.9%
202219855.1%42.9%
202398419.6%35.7%
Fond du Lac County against Wisconsin, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Fond du Lac County
Fond du Lac County98419.6%1.4 pCi/LThis county
Wisconsin, pooled72 counties, pooled20,87935.7%Not pooled+16.1 points
United States, pooled642 counties, pooled128,74033.4%Not pooled+13.8 points
Langlade Countyhighest in the state22565.8%6.0 pCi/L+46.2 points
Bayfield Countylowest in the state355.7%1.5 pCi/L−13.9 points
Dodge County, WIborders it25754.9%4.8 pCi/L+35.3 points
Calumet County, WIborders it12251.6%4.4 pCi/L+32.0 points
Washington County, WIborders it39947.9%3.8 pCi/L+28.3 points
Sheboygan County, WIborders it39942.9%3.3 pCi/L+23.3 points
Winnebago County, WIborders it51242.4%3.1 pCi/L+22.8 points
Green Lake County, WIborders it7940.5%3.4 pCi/L+20.9 points
Where Fond du Lac County's reported results fell, 2023, beside Wisconsin and the United States
ResultFond du Lac County testsFond du Lac County shareWisconsin shareU.S. shareAgainst Wisconsin
Under 2 pCi/L61262.2%41.4%41.4%+20.8 points
2 to 4 pCi/L17918.2%23.0%25.2%−4.8 points
4 pCi/L and above19319.6%35.7%33.4%−16.1 points
Fond du Lac 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
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
Wood County64 of 6920818.3%1.4 pCi/L
Pepin County65 of 696515.4%1.2 pCi/L
Marquette County66 of 694015.0%1.3 pCi/L
Juneau County67 of 695010.0%1.1 pCi/L
Fond du Lac County radon tests by year, against Wisconsin's pooled share
YearTestsAt or above 4 pCi/LMedianHighestWisconsin, pooledChange from the row before
202398419.6%1.4 pCi/L43.4 pCi/L35.7%−35.5 points
202219855.1%4.5 pCi/L32.5 pCi/L42.9%+13.4 points
202126441.7%3.5 pCi/L57.5 pCi/L39.9%−3.6 points
202023245.3%3.6 pCi/L31.4 pCi/L27.0%−4.9 points
201925750.2%4.0 pCi/L39.9 pCi/L42.9%+0.2 points
201717050.0%4.0 pCi/L81.3 pCi/L44.8%−3.5 points
201631453.5%4.0 pCi/L79.9 pCi/L45.2%+1.4 points
201533852.1%4.3 pCi/L86.3 pCi/L51.6%−4.2 points
201437356.3%4.6 pCi/L95.9 pCi/L51.1%First on file

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

Fond du Lac County, Geology

The ground under Fond du Lac County

Predicted

Most of the ground under Fond du Lac County is one class on USGS's geologic map: 89.4% of its land is high radon potential, with 10.6% moderate. The map puts 89.4% of Fond du Lac County in the area it calls Eastern Ridges and Lowlands and 10.6% in Green Bay Lobe. 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 Fond du Lac County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Eastern Ridges and LowlandsGlacial deposits derived from Ordovician carbonate rocks.High1289.4%
Green Bay LobeGlacial deposits derived from carbonate and igneous rocks.Moderate1010.6%

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

Fond du Lac County beside the ground around it

Fond du Lac County has more high-potential ground than Wisconsin as a whole: 89.4% 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: Fond du Lac County, the 6 counties bordering it and Wisconsin
AreaEPA zoneLow potentialModerate potentialHigh potential
Fond du Lac CountyZone 1None10.6%89.4%
Dodge CountyZone 1NoneNone100%
Winnebago CountyZone 2None81.5%18.5%
Green Lake CountyZone 1None57.5%42.5%
Calumet CountyZone 2None72.2%27.8%
Sheboygan CountyZone 251.7%None47.9%
Washington 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

Fond du Lac County, Local resources

Radon testing and mitigation in Fond du Lac 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

Fond du Lac County, Questions

Questions about radon in Fond du Lac County

Are radon levels high in Fond du Lac County?

In 2023, 19.6% of the radon tests reported to CDC for Fond du Lac County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.4 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 61 reported a higher share; pooled, the state comes to 35.7%.

Which counties border Fond du Lac County?

Fond du Lac County borders 6 counties: Dodge County, Winnebago County, Green Lake County, Calumet County, Sheboygan County and Washington County.

Products

Fond du Lac County, Products

Testing a home in Fond du Lac County

In Fond du Lac County, 19.6% of 984 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Fond du Lac 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

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

Explore

Fond du Lac County, Bordering counties

Counties bordering Fond du Lac County

Calculated by Radon411

Fond du Lac County, Cities and towns

Cities and towns in Fond du Lac County

Fond du Lac County's population has barely moved since 2020: 104,669 residents on July 1, 2025 against 104,159 then, by the Census Bureau's estimates. That works out to 145 people per square mile of land. Its largest town, Fond du Lac, has 44,541 residents, 42.6% of the total. Testing is reported here more often than across the state: CDC's 984 reported tests for 2023 come to 9.4 for every 1,000 residents (2025 estimate), against 3.5 for Wisconsin.

From Fond du Lac to Fairwater, CDC publishes no figure by town: each reads Fond du Lac County's.

The 12 largest cities and towns in Fond du Lac County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Fond du Lac44,541−0.4%42.6%
Waupunextends beyond Fond du Lac County11,150−3.7%Counted whole
Ripon7,738−1.5%7.4%
North Fond du Lac5,425+1.5%5.2%
Kewaskumextends beyond Fond du Lac County4,561+5.8%Counted whole
Campbellsport2,034+6.8%1.9%
Oakfield1,065+0.9%1.0%
Rosendale1,042−0.4%1.0%
Eden917+3.0%0.9%
Brandon875−0.7%0.8%
Mount Calvary492+0.4%0.5%
St. Cloud491+0.4%0.5%
  • Fairwater

13 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). A place that extends beyond Fond du Lac County is counted whole, so it has no share.

Fond du Lac County, Homes

Homes in Fond du Lac County

Of Fond du Lac County's 45,908 homes, 70% are detached houses, against 66% across Wisconsin; 16% are in buildings of five or more homes. Half of its homes were built before 1971, close to Wisconsin's 1975: 39% date from before 1960 and 18% from 2000 or later. 70% 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 Fond du Lac County, Wisconsin, 2019 to 2023
HomesFond du Lac CountyWisconsin
Housing units45,9082,750,750
Detached houses70%66%
In buildings of 5 or more16%17%
Mobile homes4%3%
Built before 196039%34%
Built since 200018%20%
Middle year built19711975
Owner-occupied70%68%

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