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Radon Levels in Winneshiek County, Iowa

EPA puts Winneshiek County in Zone 1, its highest radon zone, and high results are common there: 66.4% of the 1,071 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    66.4%

    7.9 pts above IA

    Winneshiek
    66.4%
    Iowa
    58.5%

    1,071 tests, 2008 to 2017

  • Median result

    6.2pCi/L

    Action level reached

    Winneshiek
    6.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,071

    20th of 99 by tests

    Winneshiek
    1,071
    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

    46 of 99

    Middle half

    Winneshiek
    66.4%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Winneshiek County

Starts at Winneshiek County's median, 6.2 pCi/L

6.2pCi/L

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

EPA’s reading of 6.2 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. Winneshiek County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Winneshiek County, At a glance

Winneshiek County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Winneshiek 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 Winneshiek County, 2008 to 2017, laboratory

Reported results by concentration band, Winneshiek County, 2008 to 2017, laboratory
Under 2 pCi/L: 17%2 to 4 pCi/L: 17%4 pCi/L and above: 66%

Of 1,071 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Winneshiek County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L18317.1%
2 to 4 pCi/L17716.5%
4 pCi/L and above71166.4%
What these figures count

These are the 1,071 tests reported to CDC for Winneshiek 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

Winneshiek County, Compared

Winneshiek County radon figures, compared

Calculated by Radon411

More than half: 66.4% of the 1,071 radon tests reported to CDC for Winneshiek County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 46th of 99 Iowa counties with 30 or more tests for the same period. That is 7.9 points above the 58.5% pooled from 99 Iowa counties.

The median result, 6.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 106.3 pCi/L. The rest split 17.1% under 2 pCi/L and 16.5% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 66.4% share point the same way here.

1 of its 7 bordering counties with figures ran higher, led by Allamakee County at 73.2%; Chickasaw County reported 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 Winneshiek County went from 1,117 tests (2005 to 2014) to 1,071 (2008 to 2017), the share going from 68.8% to 66.4%.

Nationally, every county with a figure for the same period pools to 35.7%; Winneshiek County sits 30.7 points above it. CDC also counts 118 tests taken after mitigation in Winneshiek County for the same period: tests in homes where a fix was already in.

Winneshiek County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Winneshiek County
Winneshiek County1,07166.4%6.2 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−7.9 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−30.7 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+17.8 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−40.5 points
Allamakee County, IAborders it49273.2%7.0 pCi/L+6.8 points
Fillmore County, MNborders it1,24264.1%6.1 pCi/L−2.3 points
Fayette County, IAborders it74662.7%5.6 pCi/L−3.7 points
Clayton County, IAborders it31062.6%5.8 pCi/L−3.8 points
Howard County, IAborders it38861.3%5.9 pCi/L−5.1 points
Houston County, MNborders it88659.6%5.1 pCi/L−6.8 points
Chickasaw County, IAborders it49859.0%4.9 pCi/L−7.4 points
Where Winneshiek County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultWinneshiek County testsWinneshiek County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L18317.1%21.8%39.6%−4.7 points
2 to 4 pCi/L17716.5%19.7%24.7%−3.2 points
4 pCi/L and above71166.4%58.5%35.7%+7.9 points
Winneshiek 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
Montgomery County41 of 9923367.4%6.1 pCi/L
Marion County42 of 991,15167.3%6.0 pCi/L
Osceola County43 of 9912267.2%6.8 pCi/L
Grundy County44 of 9950166.9%6.9 pCi/L
Wright County45 of 9929266.8%6.2 pCi/L
Winneshiek County46 of 991,07166.4%6.2 pCi/L
Kossuth County47 of 9943466.1%5.7 pCi/L
Warren County48 of 991,51366.0%6.3 pCi/L
Adams County49 of 998165.4%6.1 pCi/L
Hancock County50 of 9964064.5%5.5 pCi/L
Polk County51 of 9910,94564.4%5.6 pCi/L
Winneshiek County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 20171,07166.4%6.2 pCi/L106.3 pCi/L58.5%−1.2 points
2007 to 20161,10867.6%6.3 pCi/L106.3 pCi/L58.6%−0.8 points
2006 to 20151,14968.4%6.4 pCi/L106.3 pCi/L59.4%−0.4 points
2005 to 20141,11768.8%6.5 pCi/L106.3 pCi/L59.6%First on file

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

Winneshiek County, Geology

The ground under Winneshiek County

Predicted

USGS's geologic map puts all of Winneshiek County's mapped land in one class: high radon potential. The map puts 77.3% of Winneshiek County in the area it calls Paleozoic Plateau and 22.7% in Iowan Surface. USGS gives the first a radon index of 13 and the second 12, both in the high band (12 to 17).

USGS's geologic areas under Winneshiek County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Paleozoic PlateauOrdovician carbonate and Cambrian sandstone bedrock covered by varying amounts of Quaternary glacial deposits and loess.High1377.3%
Iowan SurfacePre-Illinoian glaical deposits and loess.High1222.7%

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

Winneshiek County beside the ground around it

On high-potential ground Winneshiek County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Chickasaw County comes nearest at 100%.

Share of land by USGS radon potential: Winneshiek County, the 7 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Winneshiek CountyZone 1NoneNone100%
Howard CountyZone 1NoneNone100%
Allamakee CountyZone 1NoneNone100%
Fillmore County, MNZone 1NoneNone100%
Houston County, MNZone 1NoneNone100%
Chickasaw CountyZone 1NoneNone100%
Fayette CountyZone 1NoneNone100%
Clayton CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Winneshiek County, Local resources

Radon testing and mitigation in Winneshiek County

Listed radon businesses with an address in Winneshiek County:

Listed radon professionals by town: Decorah

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

Winneshiek County, Questions

Questions about radon in Winneshiek County

Are radon levels high in Winneshiek County?

Over the 2008 to 2017 laboratory totals, 66.4% of the radon tests reported to CDC for Winneshiek County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.2 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 45 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Winneshiek County?

Winneshiek County borders 7 counties: Howard County, IA, Allamakee County, IA, Fillmore County, MN, Houston County, MN, Chickasaw County, IA, Fayette County, IA and Clayton County, IA.

Products

Winneshiek County, Products

Testing a home in Winneshiek County

In Winneshiek County, 66.4% of 1,071 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 Winneshiek 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

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

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Winneshiek County, Bordering counties

Counties bordering Winneshiek County

Calculated by Radon411

Winneshiek County, Cities and towns

Cities and towns in Winneshiek County

About 19,733 people live in Winneshiek County by the Census Bureau's estimate for July 1, 2025, 313 fewer than in 2020 (−1.6%). That works out to 29 people per square mile of land. Its largest town, Decorah, has 7,417 residents, 37.6% of the total. Together its 8 incorporated places hold 52.7% of those residents; the other 47.3% live outside any of them. Testing is reported here more often than across the state: CDC's 1,071 reported tests for 2008 to 2017 come to 54.3 for every 1,000 residents (2025 estimate), against 29.4 for Iowa.

From Decorah to Jackson Junction, CDC publishes no figure by town: each reads Winneshiek County's.

The cities and towns in Winneshiek County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Decorah7,417−2.2%37.6%
Calmar1,098−2.8%5.6%
Ossian775−3.2%3.9%
Spillville369−3.9%1.9%
Fort Atkinson301−2.3%1.5%
Ridgeway267−2.9%1.4%
Castalia142−2.1%0.7%
Jackson Junction39+5.4%0.2%

8 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).

Winneshiek County, Homes

Homes in Winneshiek County

Winneshiek County is a place of houses on their own lots: 82% of its 9,011 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1960 (1971 for Iowa), and 50% date from before 1960. Owners live in 76% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Winneshiek County, Iowa, 2019 to 2023
HomesWinneshiek CountyIowa
Housing units9,0111,427,175
Detached houses82%72%
In buildings of 5 or more6%14%
Mobile homes2%3%
Built before 196050%39%
Built since 200017%21%
Middle year built19601971
Owner-occupied76%72%

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