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Radon Levels in Madison County, Iowa

EPA puts Madison County in Zone 1, its highest radon zone, and high results are common there: 62.3% of the 318 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

    62.3%

    3.8 pts above IA

    Madison
    62.3%
    Iowa
    58.5%

    318 tests, 2008 to 2017

  • Median result

    6.0pCi/L

    Action level reached

    Madison
    6.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    318

    69th of 99 by tests

    Madison
    318
    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

    56 of 99

    Middle half

    Madison
    62.3%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Madison County

Starts at Madison County's median, 6.0 pCi/L

6.0pCi/L

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

EPA’s reading of 6.0 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. Madison County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Madison County, At a glance

Madison County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Madison County, 2008 to 2017, laboratory
Under 2 pCi/L: 21%2 to 4 pCi/L: 17%4 pCi/L and above: 62%

Of 318 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Madison County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L6721.1%
2 to 4 pCi/L5316.7%
4 pCi/L and above19862.3%
What these figures count

These are the 318 tests reported to CDC for Madison 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

Madison County, Compared

Madison County radon figures, compared

Calculated by Radon411

More than half: 62.3% of the 318 radon tests reported to CDC for Madison County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 56th of 99 Iowa counties with 30 or more tests for the same period. That is 3.8 points above the 58.5% pooled from 99 Iowa counties.

The median result, 6.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 225.0 pCi/L. The rest split 21.1% under 2 pCi/L and 16.7% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 62.3% share point the same way here.

4 of its 7 bordering counties with figures ran higher, led by Adair County at 72.4%; Clarke County reported 45.8%. 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 Madison County went from 243 tests (2005 to 2014) to 318 (2008 to 2017), the share going from 64.2% to 62.3%.

Nationally, every county with a figure for the same period pools to 35.7%; Madison County sits 26.6 points above it. CDC also counts 29 tests taken after mitigation in Madison County for the same period: tests in homes where a fix was already in.

Madison County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Madison County
Madison County31862.3%6.0 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−3.8 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−26.6 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+21.9 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−36.4 points
Adair County, IAborders it9872.4%9.3 pCi/L+10.1 points
Guthrie County, IAborders it25770.8%6.9 pCi/L+8.5 points
Warren County, IAborders it1,51366.0%6.3 pCi/L+3.7 points
Polk County, IAborders it10,94564.4%5.6 pCi/L+2.1 points
Union County, IAborders it13161.8%4.9 pCi/L−0.5 points
Dallas County, IAborders it2,35258.5%4.9 pCi/L−3.8 points
Clarke County, IAborders it12045.8%3.5 pCi/L−16.5 points
Where Madison County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultMadison County testsMadison County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L6721.1%21.8%39.6%−0.7 points
2 to 4 pCi/L5316.7%19.7%24.7%−3.0 points
4 pCi/L and above19862.3%58.5%35.7%+3.8 points
Madison 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
Polk County51 of 9910,94564.4%5.6 pCi/L
Hamilton County52 of 9925264.3%5.5 pCi/L
Hardin County53 of 9934962.8%5.6 pCi/L
Fayette County54 of 9974662.7%5.6 pCi/L
Clayton County55 of 9931062.6%5.8 pCi/L
Madison County56 of 9931862.3%6.0 pCi/L
Benton County57 of 9969662.1%5.6 pCi/L
Union County58 of 9913161.8%4.9 pCi/L
Howard County59 of 9938861.3%5.9 pCi/L
Mahaska County60 of 9928861.1%5.2 pCi/L
Taylor County61 of 9923560.9%4.6 pCi/L
Madison County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201731862.3%6.0 pCi/L225.0 pCi/L58.5%+0.2 points
2007 to 201630162.1%5.8 pCi/L225.0 pCi/L58.6%−2.0 points
2006 to 201528764.1%6.4 pCi/L225.0 pCi/L59.4%−0.1 points
2005 to 201424364.2%6.1 pCi/L225.0 pCi/L59.6%First on file

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

Madison County, Geology

The ground under Madison County

Predicted

USGS's geologic map puts all of Madison County's mapped land in one class: high radon potential. All of it lies in the area the map calls Loess-Covered Drift Plains, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Madison County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High13100%

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

Madison County beside the ground around it

On high-potential ground Madison 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; Adair County comes nearest at 100%.

Share of land by USGS radon potential: Madison County, the 7 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Madison CountyZone 1NoneNone100%
Warren CountyZone 1NoneNone100%
Union CountyZone 1NoneNone100%
Clarke CountyZone 1NoneNone100%
Adair CountyZone 1NoneNone100%
Dallas CountyZone 1NoneNone100%
Polk CountyZone 1NoneNone100%
Guthrie CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Madison County, Local resources

Radon testing and mitigation in Madison County

Listed radon professionals by town: West Des Moines

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

Madison County, Questions

Questions about radon in Madison County

Are radon levels high in Madison County?

Over the 2008 to 2017 laboratory totals, 62.3% of the radon tests reported to CDC for Madison County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.0 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 55 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Madison County?

Madison County borders 7 counties: Warren County, Union County, Clarke County, Adair County, Dallas County, Polk County and Guthrie County.

Products

Madison County, Products

Testing a home in Madison County

In Madison County, 62.3% of 318 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 Madison 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

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

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Madison County, Bordering counties

Counties bordering Madison County

Calculated by Radon411

Madison County, Cities and towns

Cities and towns in Madison County

The Census Bureau estimates 17,270 residents in Madison County for July 1, 2025, 639 more than in 2020 (+3.8%). That works out to 31 people per square mile of land. West Des Moines, the largest place on its list (74,224 residents in all), extends beyond Madison County, so no share of the total is worked out for it. Reported testing is thin here: 318 tests over 2008 to 2017, or 18.4 for every 1,000 residents (2025 estimate), where Iowa as a whole comes to 29.4.

From West Des Moines to Bevington, CDC publishes no figure by town: each reads Madison County's.

The cities and towns in Madison County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
West Des Moinesextends beyond Madison County74,224+7.6%Counted whole
Winterset5,520+2.4%32.0%
Earlham1,396−1.2%8.1%
St. Charles641−0.6%3.7%
Truro509+0.6%2.9%
Patterson176+0.6%1.0%
East Peru119+6.3%0.7%
Macksburg103+5.1%0.6%
Bevingtonextends beyond Madison County60+5.3%Counted whole

9 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 Madison County is counted whole, so it has no share.

Madison County, Homes

Homes in Madison County

Madison County is a place of houses on their own lots: 85% of its 7,031 homes are detached single-family houses, against 72% across Iowa. Half of its homes were built before 1977, close to Iowa's 1971: 34% date from before 1960 and 28% from 2000 or later. Owners live in 81% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Madison County, Iowa, 2019 to 2023
HomesMadison CountyIowa
Housing units7,0311,427,175
Detached houses85%72%
In buildings of 5 or more4%14%
Mobile homes4%3%
Built before 196034%39%
Built since 200028%21%
Middle year built19771971
Owner-occupied81%72%

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