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Radon Levels in Monona County, Iowa

EPA puts Monona County in Zone 1, its highest radon zone, and high results are common there: 74.6% of the 603 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

    74.6%

    16.1 pts above IA

    Monona
    74.6%
    Iowa
    58.5%

    603 tests, 2008 to 2017

  • Median result

    7.0pCi/L

    Action level reached

    Monona
    7.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    603

    39th of 99 by tests

    Monona
    603
    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

    12 of 99

    Top quarter

    Monona
    74.6%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Monona County

Starts at Monona County's median, 7.0 pCi/L

7.0pCi/L

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

EPA’s reading of 7.0 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. Monona County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Monona County, At a glance

Monona County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

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

Reported results by concentration band, Monona County, 2008 to 2017, laboratory
Under 2 pCi/L: 9%2 to 4 pCi/L: 16%4 pCi/L and above: 75%

Of 603 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Monona County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L569.3%
2 to 4 pCi/L9716.1%
4 pCi/L and above45074.6%
What these figures count

These are the 603 tests reported to CDC for Monona 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

Monona County, Compared

Monona County radon figures, compared

Calculated by Radon411

More than half: 74.6% of the 603 radon tests reported to CDC for Monona County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 12th of 99 Iowa counties with 30 or more tests for the same period. That is 16.1 points above the 58.5% pooled from 99 Iowa counties.

The median result, 7.0 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 81.8 pCi/L. The rest split 9.3% under 2 pCi/L and 16.1% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 74.6% share point the same way here.

3 of its 6 bordering counties with figures ran higher, led by Burt County, NE at 79.5%; Woodbury County reported 69.2%. 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 Monona County went from 337 tests (2005 to 2014) to 603 (2008 to 2017), the share going from 77.4% to 74.6%.

Nationally, every county with a figure for the same period pools to 35.7%; Monona County sits 38.9 points above it. CDC also counts 15 tests taken after mitigation in Monona County for the same period: tests in homes where a fix was already in.

Monona County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Monona County
Monona County60374.6%7.0 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−16.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−38.9 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+9.6 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−48.7 points
Burt County, NEborders it40579.5%8.6 pCi/L+4.9 points
Thurston County, NEborders it11477.2%7.0 pCi/L+2.6 points
Crawford County, IAborders it37374.8%7.0 pCi/L+0.2 points
Ida County, IAborders it39971.7%7.4 pCi/L−2.9 points
Harrison County, IAborders it36769.8%6.2 pCi/L−4.8 points
Woodbury County, IAborders it3,54169.2%6.1 pCi/L−5.4 points
Where Monona County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultMonona County testsMonona County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L569.3%21.8%39.6%−12.5 points
2 to 4 pCi/L9716.1%19.7%24.7%−3.6 points
4 pCi/L and above45074.6%58.5%35.7%+16.1 points
Monona 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
Lyon County7 of 9923777.6%8.3 pCi/L
Carroll County8 of 9959477.6%7.8 pCi/L
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
Monona County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201760374.6%7.0 pCi/L81.8 pCi/L58.5%+0.2 points
2007 to 201657174.4%6.9 pCi/L57.3 pCi/L58.6%−0.6 points
2006 to 201544875.0%7.5 pCi/L57.3 pCi/L59.4%−2.4 points
2005 to 201433777.4%8.3 pCi/L57.3 pCi/L59.6%First on file

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

Monona County, Geology

The ground under Monona County

Predicted

USGS's geologic map puts all of Monona 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 Monona County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High1399.8%

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

Monona County beside the ground around it

On high-potential ground Monona 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; Harrison County comes nearest at 100%.

Share of land by USGS radon potential: Monona County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Monona CountyZone 1NoneNone100%
Burt County, NEZone 1NoneNone100%
Woodbury CountyZone 1NoneNone100%
Harrison CountyZone 1NoneNone100%
Crawford CountyZone 1NoneNone100%
Ida CountyZone 1NoneNone100%
Thurston County, NEZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Monona County, Local resources

Radon testing and mitigation in Monona County

Listed radon professionals by town: Whiting

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

Monona County, Questions

Questions about radon in Monona County

Are radon levels high in Monona County?

Over the 2008 to 2017 laboratory totals, 74.6% of the radon tests reported to CDC for Monona County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 7.0 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 11 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Monona County?

Monona County borders 6 counties: Burt County, NE, Woodbury County, IA, Harrison County, IA, Crawford County, IA, Ida County, IA and Thurston County, NE.

Products

Monona County, Products

Testing a home in Monona County

In Monona County, 74.6% of 603 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 Monona 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

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

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Monona County, Bordering counties

Counties bordering Monona County

Calculated by Radon411

Monona County, Cities and towns

Cities and towns in Monona County

About 8,539 people live in Monona County by the Census Bureau's estimate for July 1, 2025, 207 fewer than in 2020 (−2.4%). That works out to 12 people per square mile of land. Its largest town, Onawa, has 2,821 residents, 33.0% of the total. Together its 10 incorporated places hold 68.3% of those residents; the other 31.7% live outside any of them. Testing is reported here more often than across the state: CDC's 603 reported tests for 2008 to 2017 come to 70.6 for every 1,000 residents (2025 estimate), against 29.4 for Iowa.

From Onawa to Rodney, CDC publishes no figure by town: each reads Monona County's.

The cities and towns in Monona County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Onawa2,821−3.0%33.0%
Mapleton1,135−2.1%13.3%
Whiting738−1.3%8.6%
Ute329−3.5%3.9%
Blencoe226−2.6%2.6%
Moorhead190−4.0%2.2%
Soldier179−2.2%2.1%
Castana103−1.9%1.2%
Turin69−2.8%0.8%
Rodney43−4.4%0.5%

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).

Monona County, Homes

Homes in Monona County

Monona County is a place of houses on their own lots: 85% of its 4,390 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1955 (1971 for Iowa), and 55% date from before 1960. Owners live in 76% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Monona County, Iowa, 2019 to 2023
HomesMonona CountyIowa
Housing units4,3901,427,175
Detached houses85%72%
In buildings of 5 or more6%14%
Mobile homes6%3%
Built before 196055%39%
Built since 200011%21%
Middle year built19551971
Owner-occupied76%72%

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