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Radon Levels in Franklin County, Iowa

EPA puts Franklin County in Zone 1, its highest radon zone, and high results are common there: 73.5% of the 313 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

    73.5%

    15.0 pts above IA

    Franklin
    73.5%
    Iowa
    58.5%

    313 tests, 2008 to 2017

  • Median result

    6.2pCi/L

    Action level reached

    Franklin
    6.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    313

    70th of 99 by tests

    Franklin
    313
    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

    14 of 99

    Top quarter

    Franklin
    73.5%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Franklin County

Starts at Franklin 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. Franklin County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Franklin County, At a glance

Franklin County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Franklin County, 2008 to 2017, laboratory
Under 2 pCi/L: 12%2 to 4 pCi/L: 14%4 pCi/L and above: 74%

Of 313 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Franklin County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L3812.1%
2 to 4 pCi/L4514.4%
4 pCi/L and above23073.5%
What these figures count

These are the 313 tests reported to CDC for Franklin 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

Franklin County, Compared

Franklin County radon figures, compared

Calculated by Radon411

More than half: 73.5% of the 313 radon tests reported to CDC for Franklin County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 14th of 99 Iowa counties with 30 or more tests for the same period. That is 15.0 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 49.0 pCi/L. The rest split 12.1% under 2 pCi/L and 14.4% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 73.5% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is Grundy County at 66.9%, the lowest Cerro Gordo County at 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 Franklin County went from 223 tests (2005 to 2014) to 313 (2008 to 2017), the share going from 74.9% to 73.5%.

Nationally, every county with a figure for the same period pools to 35.7%; Franklin County sits 37.8 points above it. CDC also counts 58 tests taken after mitigation in Franklin County for the same period: tests in homes where a fix was already in.

Franklin County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Franklin County
Franklin County31373.5%6.2 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−15.0 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−37.8 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+10.7 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−47.6 points
Grundy County, IAborders it50166.9%6.9 pCi/L−6.6 points
Wright County, IAborders it29266.8%6.2 pCi/L−6.7 points
Hancock County, IAborders it64064.5%5.5 pCi/L−9.0 points
Hamilton County, IAborders it25264.3%5.5 pCi/L−9.2 points
Hardin County, IAborders it34962.8%5.6 pCi/L−10.7 points
Butler County, IAborders it37759.9%5.2 pCi/L−13.6 points
Floyd County, IAborders it69759.5%5.1 pCi/L−14.0 points
Cerro Gordo County, IAborders it1,66259.0%4.8 pCi/L−14.5 points
Where Franklin County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultFranklin County testsFranklin County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L3812.1%21.8%39.6%−9.7 points
2 to 4 pCi/L4514.4%19.7%24.7%−5.3 points
4 pCi/L and above23073.5%58.5%35.7%+15.0 points
Franklin 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
Cass County9 of 9932777.4%8.1 pCi/L
Sac County10 of 9949176.6%7.0 pCi/L
Crawford County11 of 9937374.8%7.0 pCi/L
Monona County12 of 9960374.6%7.0 pCi/L
Cherokee County13 of 9979574.5%7.6 pCi/L
Franklin County14 of 9931373.5%6.2 pCi/L
Jasper County15 of 9974673.3%8.2 pCi/L
Allamakee County16 of 9949273.2%7.0 pCi/L
Adair County17 of 999872.4%9.3 pCi/L
Buena Vista County18 of 9968872.1%6.9 pCi/L
Winnebago County19 of 9982971.9%6.7 pCi/L
Franklin County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201731373.5%6.2 pCi/L49.0 pCi/L58.5%−1.0 points
2007 to 201627874.5%6.3 pCi/L40.6 pCi/L58.6%+0.2 points
2006 to 201526574.3%6.3 pCi/L47.4 pCi/L59.4%−0.6 points
2005 to 201422374.9%6.7 pCi/L47.4 pCi/L59.6%First on file

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

Franklin County, Geology

The ground under Franklin County

Predicted

USGS's geologic map puts all of Franklin County's mapped land in one class: high radon potential. The map puts 52.9% of Franklin County in the area it calls Iowan Surface and 47.1% in Des Moines Lobe. USGS gives both a radon index of 12, in the high band (12 to 17).

USGS's geologic areas under Franklin County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Iowan SurfacePre-Illinoian glaical deposits and loess.High1252.9%
Des Moines LobeCalcareous loamy till derived from shale, limestone, dolomite, sandstone.High1247.1%

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

Franklin County beside the ground around it

On high-potential ground Franklin County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 8 counties that border it, none has as large a share of high-potential ground; Butler County comes nearest at 100%.

Share of land by USGS radon potential: Franklin County, the 8 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Franklin CountyZone 1NoneNone100%
Cerro Gordo CountyZone 1NoneNone100%
Butler CountyZone 1NoneNone100%
Wright CountyZone 1NoneNone100%
Hardin CountyZone 1NoneNone100%
Floyd CountyZone 1NoneNone100%
Hancock CountyZone 1NoneNone100%
Grundy CountyZone 1NoneNone100%
Hamilton CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Franklin County, Local resources

Radon testing and mitigation in Franklin 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

Franklin County, Questions

Questions about radon in Franklin County

Are radon levels high in Franklin County?

Over the 2008 to 2017 laboratory totals, 73.5% of the radon tests reported to CDC for Franklin 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, 13 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Franklin County?

Franklin County borders 8 counties: Cerro Gordo County, Butler County, Wright County, Hardin County, Floyd County, Hancock County, Grundy County and Hamilton County.

Products

Franklin County, Products

Testing a home in Franklin County

In Franklin County, 73.5% of 313 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 Franklin 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

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

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Franklin County, Bordering counties

Counties bordering Franklin County

Calculated by Radon411

Franklin County, Cities and towns

Cities and towns in Franklin County

About 9,868 people live in Franklin County by the Census Bureau's estimate for July 1, 2025, 123 fewer than in 2020 (−1.2%). That works out to 17 people per square mile of land. Its largest town, Hampton, has 4,264 residents, 43.2% of the total. CDC's 313 reported tests for 2008 to 2017 work out to 31.7 per 1,000 residents (2025 estimate), close to Iowa's 29.4.

From Hampton to Popejoy, CDC publishes no figure by town: each reads Franklin County's.

The cities and towns in Franklin County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Hampton4,264−1.4%43.2%
Ackleyextends beyond Franklin County1,530−3.8%Counted whole
Sheffield1,103−1.3%11.2%
Dowsextends beyond Franklin County513−2.3%Counted whole
Latimer470−1.7%4.8%
Coulter215−1.4%2.2%
Alexander163−2.4%1.7%
Geneva134−0.7%1.4%
Hansell83−1.2%0.8%
Popejoy75−1.3%0.8%

10 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 Franklin County is counted whole, so it has no share.

Franklin County, Homes

Homes in Franklin County

Franklin County is a place of houses on their own lots: 85% of its 4,657 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1953 (1971 for Iowa), and 61% date from before 1960. 73% 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 Franklin County, Iowa, 2019 to 2023
HomesFranklin CountyIowa
Housing units4,6571,427,175
Detached houses85%72%
In buildings of 5 or more6%14%
Mobile homes1%3%
Built before 196061%39%
Built since 20005%21%
Middle year built19531971
Owner-occupied73%72%

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