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Radon Levels in Story County, Iowa

EPA puts Story County in Zone 1, its highest radon zone, and high results are common there: 59.9% of the 2,568 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

    59.9%

    1.4 pts above IA

    Story
    59.9%
    Iowa
    58.5%

    2,568 tests, 2008 to 2017

  • Median result

    5.0pCi/L

    Action level reached

    Story
    5.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    2,568

    8th of 99 by tests

    Story
    2,568
    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

    65 of 99

    Middle half

    Story
    59.9%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Story County

Starts at Story County's median, 5.0 pCi/L

5.0pCi/L

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

EPA’s reading of 5.0 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. Story County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Story County, At a glance

Story County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Story County, 2008 to 2017, laboratory
Under 2 pCi/L: 22%2 to 4 pCi/L: 18%4 pCi/L and above: 60%

Of 2,568 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Story County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L56522.0%
2 to 4 pCi/L46418.1%
4 pCi/L and above1,53959.9%
What these figures count

These are the 2,568 tests reported to CDC for Story 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

Story County, Compared

Story County radon figures, compared

Calculated by Radon411

More than half: 59.9% of the 2,568 radon tests reported to CDC for Story County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 65th of 99 Iowa counties with 30 or more tests for the same period. That is 1.4 points above the 58.5% pooled from 99 Iowa counties.

The median result, 5.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 126.8 pCi/L. The rest split 22.0% under 2 pCi/L and 18.1% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 59.9% share point the same way here.

All 6 of its bordering counties with figures ran higher, led by Jasper County at 73.3%; the lowest of them, Hardin County, reported 62.8%. 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 Story County went from 2,072 tests (2005 to 2014) to 2,568 (2008 to 2017), the share going from 60.9% to 59.9%.

Nationally, every county with a figure for the same period pools to 35.7%; Story County sits 24.2 points above it. CDC also counts 223 tests taken after mitigation in Story County for the same period: tests in homes where a fix was already in.

Story County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Story County
Story County2,56859.9%5.0 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−1.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−24.2 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+24.3 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−34.0 points
Jasper County, IAborders it74673.3%8.2 pCi/L+13.4 points
Marshall County, IAborders it57070.2%8.2 pCi/L+10.3 points
Boone County, IAborders it1,13468.7%6.0 pCi/L+8.8 points
Polk County, IAborders it10,94564.4%5.6 pCi/L+4.5 points
Hamilton County, IAborders it25264.3%5.5 pCi/L+4.4 points
Hardin County, IAborders it34962.8%5.6 pCi/L+2.9 points
Where Story County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultStory County testsStory County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L56522.0%21.8%39.6%+0.2 points
2 to 4 pCi/L46418.1%19.7%24.7%−1.6 points
4 pCi/L and above1,53959.9%58.5%35.7%+1.4 points
Story 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
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
Butler County64 of 9937759.9%5.2 pCi/L
Story County65 of 992,56859.9%5.0 pCi/L
Floyd County66 of 9969759.5%5.1 pCi/L
Jones County67 of 9955559.3%5.1 pCi/L
Iowa County68 of 9951959.2%5.1 pCi/L
Chickasaw County69 of 9949859.0%4.9 pCi/L
Cerro Gordo County70 of 991,66259.0%4.8 pCi/L
Story County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 20172,56859.9%5.0 pCi/L126.8 pCi/L58.5%+0.4 points
2007 to 20162,47659.5%4.9 pCi/L126.8 pCi/L58.6%−0.6 points
2006 to 20152,41660.1%5.0 pCi/L126.8 pCi/L59.4%−0.8 points
2005 to 20142,07260.9%5.0 pCi/L126.8 pCi/L59.6%First on file

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

Story County, Geology

The ground under Story County

Predicted

USGS's geologic map puts all of Story County's mapped land in one class: high radon potential. 97.2% 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 Story County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Des Moines LobeCalcareous loamy till derived from shale, limestone, dolomite, sandstone.High1297.2%
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High132.8%

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

Story County beside the ground around it

On high-potential ground Story 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; Boone County comes nearest at 100%.

Share of land by USGS radon potential: Story County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Story CountyZone 1NoneNone100%
Polk CountyZone 1NoneNone100%
Marshall CountyZone 1NoneNone100%
Boone CountyZone 1NoneNone100%
Hardin CountyZone 1NoneNone100%
Hamilton CountyZone 1NoneNone100%
Jasper CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Story County, Local resources

Radon testing and mitigation in Story County

Listed radon businesses with an address in Story County:

Listed radon professionals by town: Ames, Nevada, Story City, Cambridge

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

Story County, Questions

Questions about radon in Story County

Are radon levels high in Story County?

Over the 2008 to 2017 laboratory totals, 59.9% of the radon tests reported to CDC for Story County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.0 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 64 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Story County?

Story County borders 6 counties: Polk County, Marshall County, Boone County, Hardin County, Hamilton County and Jasper County.

Products

Story County, Products

Testing a home in Story County

In Story County, 59.9% of 2,568 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 Story 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

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

Explore

Story County, Bordering counties

Counties bordering Story County

Calculated by Radon411

Story County, Cities and towns

Cities and towns in Story County

The Census Bureau estimates 101,291 residents in Story County for July 1, 2025, 2,633 more than in 2020 (+2.7%). That works out to 177 people per square mile of land. Ames alone is home to 68,220 of them, 67.4% of the total. CDC's 2,568 reported tests for 2008 to 2017 work out to 25.4 per 1,000 residents (2025 estimate), close to Iowa's 29.4.

From Ames to Sheldahl, CDC publishes no figure by town: each reads Story County's.

The 12 largest cities and towns in Story County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Ames68,220+2.6%67.4%
Nevada6,974+0.9%6.9%
Huxley4,715+9.5%4.7%
Story City3,382+0.9%3.3%
Slaterextends beyond Story County1,617+5.3%Counted whole
Gilbert1,389+15.3%1.4%
Roland1,344−1.1%1.3%
Maxwell844−1.5%0.8%
Colo838−1.1%0.8%
Cambridge827−1.1%0.8%
Zearing504−6.0%0.5%
Collins497−0.4%0.5%
  • McCallsburg
  • Kelley
  • Sheldahl (part)

15 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 Story County is counted whole, so it has no share.

Story County, Homes

Homes in Story County

Story County has 41,642 homes, and many share a building: 31% are in buildings of five or more, 53% are detached houses, against 72% across Iowa. Much of Story County is recent building: 31% of its homes have gone up since 2000 and the middle year built is 1983, against 1971 for Iowa. 56% 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 Story County, Iowa, 2019 to 2023
HomesStory CountyIowa
Housing units41,6421,427,175
Detached houses53%72%
In buildings of 5 or more31%14%
Mobile homes4%3%
Built before 196024%39%
Built since 200031%21%
Middle year built19831971
Owner-occupied56%72%

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