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Radon Levels in Winnebago County, Iowa

EPA puts Winnebago County in Zone 1, its highest radon zone, and high results are common there: 71.9% of the 829 radon tests reported to CDC (2008 to 2017, laboratory totals) 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

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  • Share at 4+ pCi/L

    71.9%

    13.4 pts above IA

    Winnebago
    71.9%
    Iowa
    58.5%

    829 tests, 2008 to 2017

  • Median result

    6.7pCi/L

    Action level reached

    Winnebago
    6.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    829

    27th of 99 by tests

    Winnebago
    829
    Polk
    10,945

    Reported to CDC before any fix, 2008 to 2017

  • 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 Iowa

    19 of 99

    Top quarter

    Winnebago
    71.9%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Winnebago County

Starts at Winnebago County's median, 6.7 pCi/L

6.7pCi/L

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

EPA’s reading of 6.7 pCi/L

At or above 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 at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Winnebago County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Winnebago County, At a glance

Winnebago County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Winnebago 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Winnebago County, 2008 to 2017, laboratory

Reported results by concentration band, Winnebago County, 2008 to 2017, laboratory
Under 2 pCi/L: 13%2 to 4 pCi/L: 15%4 pCi/L and above: 72%

Of 829 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Winnebago County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L10712.9%
2 to 4 pCi/L12615.2%
4 pCi/L and above59671.9%
What these figures count

These are the 829 tests reported to CDC for Winnebago County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Winnebago County, Compared

Winnebago County radon figures, compared

Calculated by Radon411

More than half: 71.9% of the 829 radon tests reported to CDC for Winnebago County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 19th of 99 Iowa counties with 30 or more tests for the same period. That is 13.4 points above the 58.5% pooled from 99 Iowa counties.

The median result, 6.7 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 65.0 pCi/L. The rest split 12.9% under 2 pCi/L and 15.2% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 71.9% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is Freeborn County, MN at 69.1%, the lowest Cerro Gordo County at 59.0%. Statewide for the same period, Sioux County reported the highest share (84.2%) and Decatur County the lowest (25.9%).

CDC's ten-year totals for Winnebago County went from 631 tests (2005 to 2014) to 829 (2008 to 2017), the share going from 74.5% to 71.9%.

Nationally, every county with a figure for the same period pools to 35.7%; Winnebago County sits 36.2 points above it. CDC also counts 65 tests taken after mitigation in Winnebago County for the same period: tests in homes where a fix was already in.

Winnebago County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Winnebago County
Winnebago County82971.9%6.7 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−13.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−36.2 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+12.3 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−46.0 points
Freeborn County, MNborders it81669.1%6.2 pCi/L−2.8 points
Worth County, IAborders it15467.5%6.0 pCi/L−4.4 points
Kossuth County, IAborders it43466.1%5.7 pCi/L−5.8 points
Faribault County, MNborders it32365.3%5.3 pCi/L−6.6 points
Hancock County, IAborders it64064.5%5.5 pCi/L−7.4 points
Cerro Gordo County, IAborders it1,66259.0%4.8 pCi/L−12.9 points
Where Winnebago County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultWinnebago County testsWinnebago County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L10712.9%21.8%39.6%−8.9 points
2 to 4 pCi/L12615.2%19.7%24.7%−4.5 points
4 pCi/L and above59671.9%58.5%35.7%+13.4 points
Winnebago County ranked among the 99 Iowa counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Franklin County14 of 9931373.5%6.2 pCi/L
Jasper County15 of 9974673.3%8.2 pCi/L
Allamakee County16 of 9949273.2%7.0 pCi/L
Adair County17 of 999872.4%9.3 pCi/L
Buena Vista County18 of 9968872.1%6.9 pCi/L
Winnebago County19 of 9982971.9%6.7 pCi/L
Ida County20 of 9939971.7%7.4 pCi/L
Page County21 of 9965371.7%7.2 pCi/L
Greene County22 of 9914371.3%6.2 pCi/L
Emmet County23 of 9942071.0%6.3 pCi/L
Guthrie County24 of 9925770.8%6.9 pCi/L
Winnebago County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201782971.9%6.7 pCi/L65.0 pCi/L58.5%−0.9 points
2007 to 201680272.8%6.8 pCi/L65.0 pCi/L58.6%−1.0 points
2006 to 201573873.8%6.9 pCi/L65.0 pCi/L59.4%−0.7 points
2005 to 201463174.5%7.3 pCi/L65.0 pCi/L59.6%First on file

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

Winnebago County, Geology

The ground under Winnebago County

Predicted

USGS's geologic map puts all of Winnebago County's mapped land in one class: high radon potential. All of it lies in the area the map calls Des Moines Lobe, to which USGS gives a radon index of 12, in the high band (12 to 17).

USGS's geologic areas under Winnebago County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Des Moines LobeCalcareous loamy till derived from shale, limestone, dolomite, sandstone.High12100%

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

Winnebago County beside the ground around it

On high-potential ground Winnebago County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Cerro Gordo County comes nearest at 100%.

Share of land by USGS radon potential: Winnebago County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Winnebago CountyZone 1NoneNone100%
Hancock CountyZone 1NoneNone100%
Faribault County, MNZone 1NoneNone100%
Worth CountyZone 1NoneNone100%
Freeborn County, MNZone 1NoneNone100%
Kossuth CountyZone 1NoneNone100%
Cerro Gordo CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Winnebago County, Local resources

Radon testing and mitigation in Winnebago County

What Iowa's program says
Phone
(515) 281-4928
Licensing of radon professionals
Iowa’s radon program approves applications for persons who wish to become certified to perform radon testing or credentialed to perform mitigation and laboratories that provide radon testing devices and analytical services.
Disclosure when a home is sold or rented
However, per Iowa Code chapters 543B.9 and 543B.18 and Iowa Administrative Code 193E Chapter 14 administered by the Iowa Real Estate Commission, a seller must disclose any known tests for the presence of radon and if yes, provide the date of last report and the result(s).

What it means

Winnebago County, Questions

Questions about radon in Winnebago County

Are radon levels high in Winnebago County?

Over the 2008 to 2017 laboratory totals, 71.9% of the radon tests reported to CDC for Winnebago County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.7 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 18 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Winnebago County?

Winnebago County borders 6 counties: Hancock County, IA, Faribault County, MN, Worth County, IA, Freeborn County, MN, Kossuth County, IA and Cerro Gordo County, IA.

Products

Winnebago County, Products

Testing a home in Winnebago County

In Winnebago County, 71.9% of 829 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across Iowa. In Zone 1 the year-round level in Winnebago 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

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

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Winnebago County, Bordering counties

Counties bordering Winnebago County

Calculated by Radon411

Winnebago County, Cities and towns

Cities and towns in Winnebago County

About 10,251 people live in Winnebago County by the Census Bureau's estimate for July 1, 2025, 402 fewer than in 2020 (−3.8%). That works out to 26 people per square mile of land. Forest City, the largest place on its list (4,143 residents in all), extends beyond Winnebago County, so no share of the total is worked out for it. Testing is reported here more often than across the state: CDC's 829 reported tests for 2008 to 2017 come to 80.9 for every 1,000 residents (2025 estimate), against 29.4 for Iowa.

From Forest City to Scarville, CDC publishes no figure by town: each reads Winnebago County's.

The cities and towns in Winnebago County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Forest Cityextends beyond Winnebago County4,143−3.0%Counted whole
Lake Mills2,050−4.3%20.0%
Buffalo Center829−3.4%8.1%
Thompson471−4.7%4.6%
Leland236−4.1%2.3%
Rake177−4.8%1.7%
Scarville73−6.4%0.7%

7 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 Winnebago County is counted whole, so it has no share.

Winnebago County, Homes

Homes in Winnebago County

Winnebago County is a place of houses on their own lots: 85% of its 5,080 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1961 (1971 for Iowa), and 49% date from before 1960. 74% of occupied homes are lived in by their owner (Iowa: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Winnebago County, Iowa, 2019 to 2023
HomesWinnebago CountyIowa
Housing units5,0801,427,175
Detached houses85%72%
In buildings of 5 or more7%14%
Mobile homes1%3%
Built before 196049%39%
Built since 20008%21%
Middle year built19611971
Owner-occupied74%72%

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