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Radon Levels in Union County, Iowa

EPA puts Union County in Zone 1, its highest radon zone, and high results are common there: 61.8% of the 131 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

    61.8%

    3.3 pts above IA

    Union
    61.8%
    Iowa
    58.5%

    131 tests, 2008 to 2017

  • Median result

    4.9pCi/L

    Action level reached

    Union
    4.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    131

    86th of 99 by tests

    Union
    131
    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

    58 of 99

    Middle half

    Union
    61.8%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Union County

Starts at Union County's median, 4.9 pCi/L

4.9pCi/L

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

EPA’s reading of 4.9 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. Union County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Union County, At a glance

Union County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Union County, 2008 to 2017, laboratory
Under 2 pCi/L: 19%2 to 4 pCi/L: 19%4 pCi/L and above: 62%

Of 131 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Union County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2519.1%
2 to 4 pCi/L2519.1%
4 pCi/L and above8161.8%
What these figures count

These are the 131 tests reported to CDC for Union 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

Union County, Compared

Union County radon figures, compared

Calculated by Radon411

More than half: 61.8% of the 131 radon tests reported to CDC for Union County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 58th of 99 Iowa counties with 30 or more tests for the same period. That is 3.3 points above the 58.5% pooled from 99 Iowa counties.

The median result, 4.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 58.5 pCi/L. The rest split 19.1% under 2 pCi/L and 19.1% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 61.8% share point the same way here.

3 of its 7 bordering counties with figures ran higher, led by Adair County at 72.4%; Decatur County reported 25.9%. 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 Union County went from 89 tests (2005 to 2014) to 131 (2008 to 2017), the share going from 69.7% to 61.8%.

Nationally, every county with a figure for the same period pools to 35.7%; Union County sits 26.1 points above it. CDC also counts 8 tests taken after mitigation in Union County for the same period: tests in homes where a fix was already in.

Union County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Union County
Union County13161.8%4.9 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−3.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−26.1 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+22.4 points
Van Buren Countylowest in the state5632.1%2.3 pCi/L−29.7 points
Adair County, IAborders it9872.4%9.3 pCi/L+10.6 points
Adams County, IAborders it8165.4%6.1 pCi/L+3.6 points
Madison County, IAborders it31862.3%6.0 pCi/L+0.5 points
Taylor County, IAborders it23560.9%4.6 pCi/L−0.9 points
Clarke County, IAborders it12045.8%3.5 pCi/L−16.0 points
Ringgold County, IAborders it8728.7%2.6 pCi/L−33.1 points
Decatur County, IAborders it8525.9%2.5 pCi/L−35.9 points
Where Union County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultUnion County testsUnion County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L2519.1%21.8%39.6%−2.7 points
2 to 4 pCi/L2519.1%19.7%24.7%−0.6 points
4 pCi/L and above8161.8%58.5%35.7%+3.3 points
Union 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
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
Cedar County62 of 9976560.4%5.0 pCi/L
Keokuk County63 of 9921460.3%5.2 pCi/L
Union County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201713161.8%4.9 pCi/L58.5 pCi/L58.5%−4.2 points
2007 to 201610066.0%5.3 pCi/L58.5 pCi/L58.6%−6.2 points
2006 to 20159072.2%6.0 pCi/L58.5 pCi/L59.4%+2.5 points
2005 to 20148969.7%5.6 pCi/L58.5 pCi/L59.6%First on file

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

Union County, Geology

The ground under Union County

Predicted

USGS's geologic map puts all of Union 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 Union 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.

Union County beside the ground around it

On high-potential ground Union 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: Union County, the 7 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Union CountyZone 1NoneNone100%
Adair CountyZone 1NoneNone100%
Ringgold CountyZone 1NoneNone100%
Adams CountyZone 1NoneNone100%
Clarke CountyZone 1NoneNone100%
Madison CountyZone 1NoneNone100%
Taylor CountyZone 1NoneNone100%
Decatur CountyZone 1None8.6%91.4%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Union County, Local resources

Radon testing and mitigation in Union 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

Union County, Questions

Questions about radon in Union County

Are radon levels high in Union County?

Over the 2008 to 2017 laboratory totals, 61.8% of the radon tests reported to CDC for Union County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.9 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 57 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Union County?

Union County borders 7 counties: Adair County, Ringgold County, Adams County, Clarke County, Madison County, Taylor County and Decatur County.

Products

Union County, Products

Testing a home in Union County

In Union County, 61.8% of 131 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 Union 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

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

Explore

Union County, Bordering counties

Counties bordering Union County

Calculated by Radon411

Union County, Cities and towns

Cities and towns in Union County

About 11,829 people live in Union County by the Census Bureau's estimate for July 1, 2025, 301 fewer than in 2020 (−2.5%). That works out to 28 people per square mile of land. Creston alone is home to 7,335 of them, 62.0% of the total. Reported testing is thin here: 131 tests over 2008 to 2017, or 11.1 for every 1,000 residents (2025 estimate), where Iowa as a whole comes to 29.4.

From Creston to Thayer, CDC publishes no figure by town: each reads Union County's.

The cities and towns in Union County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Creston7,335−2.6%62.0%
Afton859−0.8%7.3%
Lorimor375−2.8%3.2%
Cromwell103−1.9%0.9%
Arispe94−2.1%0.8%
Shannon Cityextends beyond Union County71−2.7%Counted whole
Thayer49−2.0%0.4%

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 Union County is counted whole, so it has no share.

Union County, Homes

Homes in Union County

Union County is a place of houses on their own lots: 76% of its 5,790 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. 72% 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 Union County, Iowa, 2019 to 2023
HomesUnion CountyIowa
Housing units5,7901,427,175
Detached houses76%72%
In buildings of 5 or more9%14%
Mobile homes5%3%
Built before 196049%39%
Built since 200011%21%
Middle year built19611971
Owner-occupied72%72%

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