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Radon Levels in Grundy County, Iowa

EPA puts Grundy County in Zone 1, its highest radon zone, and high results are common there: 66.9% of the 501 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

    66.9%

    8.4 pts above IA

    Grundy
    66.9%
    Iowa
    58.5%

    501 tests, 2008 to 2017

  • Median result

    6.9pCi/L

    Action level reached

    Grundy
    6.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    501

    47th of 99 by tests

    Grundy
    501
    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

    44 of 99

    Middle half

    Grundy
    66.9%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Grundy County

Starts at Grundy County's median, 6.9 pCi/L

6.9pCi/L

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

EPA’s reading of 6.9 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. Grundy County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Grundy County, At a glance

Grundy County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Grundy County, 2008 to 2017, laboratory
Under 2 pCi/L: 21%2 to 4 pCi/L: 12%4 pCi/L and above: 67%

Of 501 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Grundy County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L10821.6%
2 to 4 pCi/L5811.6%
4 pCi/L and above33566.9%
What these figures count

These are the 501 tests reported to CDC for Grundy 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

Grundy County, Compared

Grundy County radon figures, compared

Calculated by Radon411

More than half: 66.9% of the 501 radon tests reported to CDC for Grundy County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 44th of 99 Iowa counties with 30 or more tests for the same period. That is 8.4 points above the 58.5% pooled from 99 Iowa counties.

The median result, 6.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 95.9 pCi/L. The rest split 21.6% under 2 pCi/L and 11.6% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 66.9% share point the same way here.

3 of its 6 bordering counties with figures ran higher, led by Franklin County at 73.5%; Black Hawk County reported 48.4%. 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 Grundy County went from 372 tests (2005 to 2014) to 501 (2008 to 2017), the share going from 68.8% to 66.9%.

Nationally, every county with a figure for the same period pools to 35.7%; Grundy County sits 31.2 points above it. CDC also counts 96 tests taken after mitigation in Grundy County for the same period: tests in homes where a fix was already in.

Grundy County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Grundy County
Grundy County50166.9%6.9 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−8.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−31.2 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+17.3 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−41.0 points
Franklin County, IAborders it31373.5%6.2 pCi/L+6.6 points
Marshall County, IAborders it57070.2%8.2 pCi/L+3.3 points
Tama County, IAborders it33367.9%7.0 pCi/L+1.0 points
Hardin County, IAborders it34962.8%5.6 pCi/L−4.1 points
Butler County, IAborders it37759.9%5.2 pCi/L−7.0 points
Black Hawk County, IAborders it3,22348.4%3.8 pCi/L−18.5 points
Where Grundy County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultGrundy County testsGrundy County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L10821.6%21.8%39.6%−0.2 points
2 to 4 pCi/L5811.6%19.7%24.7%−8.1 points
4 pCi/L and above33566.9%58.5%35.7%+8.4 points
Grundy 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
Tama County39 of 9933367.9%7.0 pCi/L
Worth County40 of 9915467.5%6.0 pCi/L
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
Grundy County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201750166.9%6.9 pCi/L95.9 pCi/L58.5%−0.7 points
2007 to 201644567.6%7.2 pCi/L95.9 pCi/L58.6%+0.2 points
2006 to 201542067.4%7.0 pCi/L73.0 pCi/L59.4%−1.4 points
2005 to 201437268.8%7.2 pCi/L73.0 pCi/L59.6%First on file

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

Grundy County, Geology

The ground under Grundy County

Predicted

USGS's geologic map puts all of Grundy County's mapped land in one class: high radon potential. The map puts 60.1% of Grundy County in the area it calls Loess-Covered Drift Plains and 39.9% 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 Grundy County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High1360.1%
Iowan SurfacePre-Illinoian glaical deposits and loess.High1239.9%

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

Grundy County beside the ground around it

On high-potential ground Grundy 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; Black Hawk County comes nearest at 100%.

Share of land by USGS radon potential: Grundy County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Grundy CountyZone 1NoneNone100%
Hardin CountyZone 1NoneNone100%
Black Hawk CountyZone 1NoneNone100%
Marshall CountyZone 1NoneNone100%
Tama CountyZone 1NoneNone100%
Butler CountyZone 1NoneNone100%
Franklin CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Grundy County, Local resources

Radon testing and mitigation in Grundy 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

Grundy County, Questions

Questions about radon in Grundy County

Are radon levels high in Grundy County?

Over the 2008 to 2017 laboratory totals, 66.9% of the radon tests reported to CDC for Grundy County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.9 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 43 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Grundy County?

Grundy County borders 6 counties: Hardin County, Black Hawk County, Marshall County, Tama County, Butler County and Franklin County.

Products

Grundy County, Products

Testing a home in Grundy County

In Grundy County, 66.9% of 501 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 Grundy 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

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

Explore

Grundy County, Bordering counties

Counties bordering Grundy County

Calculated by Radon411

Grundy County, Cities and towns

Cities and towns in Grundy County

Grundy County's population has barely moved since 2020: 12,361 residents on July 1, 2025 against 12,337 then, by the Census Bureau's estimates. That works out to 25 people per square mile of land. Its largest town, Grundy Center, has 2,814 residents, 22.8% of the total. Together its 9 incorporated places hold 67.0% of those residents; the other 33.0% live outside any of them. CDC's 501 reported tests for 2008 to 2017 work out to 40.5 per 1,000 residents (2025 estimate), close to Iowa's 29.4.

From Grundy Center to Morrison, CDC publishes no figure by town: each reads Grundy County's.

The cities and towns in Grundy County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Grundy Center2,814+0.3%22.8%
Reinbeck1,668−0.1%13.5%
Dike1,299−0.2%10.5%
Conrad1,086−0.5%8.8%
Wellsburg711−1.1%5.8%
Holland260−1.5%2.1%
Stout191+0.5%1.5%
Beaman155−1.9%1.3%
Morrison100+2.0%0.8%

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).

Grundy County, Homes

Homes in Grundy County

Grundy County is a place of houses on their own lots: 84% of its 5,489 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 84% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Grundy County, Iowa, 2019 to 2023
HomesGrundy CountyIowa
Housing units5,4891,427,175
Detached houses84%72%
In buildings of 5 or more5%14%
Mobile homes3%3%
Built before 196050%39%
Built since 200012%21%
Middle year built19601971
Owner-occupied84%72%

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