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Radon Levels in Monroe County, Missouri

EPA puts Monroe County in Zone 2, its middle radon zone, and only 1 radon test from it is on file with CDC (2023). 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

    24.3%

    6.5 pts below MO

    Monroe
    24.3%
    Missouri
    30.8%

    37 tests, 2007 to 2016

  • Median result

    1.7pCi/L

    Below action level

    Monroe
    1.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2007 to 2016

  • Tests reported

    37

    62nd of 72 by tests

    Monroe
    37
    St. Louis
    16,567

    Reported to CDC before any fix, 2007 to 2016

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Missouri

    51 of 72

    Middle half

    Monroe
    24.3%
    Atchison
    70.5%

    By share, of 72 with 30+ tests

Read a result for Monroe County

Starts at Monroe County's median, 1.7 pCi/L

1.7pCi/L

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

EPA’s reading of 1.7 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Monroe County's median reported result, 2007 to 2016.

Interpret this reading

The data

Monroe County, At a glance

Monroe County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Monroe County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Monroe County, 2023

Share of reported tests at or above 4 pCi/L, by year, Monroe County
Share of reported tests at or above 4 pCi/L, by year, Monroe County
YearShare of reported tests at or above 4 pCi/L
2014100.0%
20150.0%
20160.0%
2018100.0%
20190.0%
20200.0%
20220.0%
2023100.0%

2023: 100.0%. Across these years the share ran from 0.0% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 1 test was reported to CDC for Monroe County over 2023, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.

Measured: CDC tracking data. Figure above: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Monroe County, Compared

Monroe County radon figures, compared

Calculated by Radon411

Monroe County's 37 reported tests over the 2007 to 2016 laboratory totals had a middle value of 1.7 pCi/L and a maximum of 14.0 pCi/L, and 24.3% reached 4 pCi/L. Missouri as a whole (115 Missouri counties, pooled) comes to 30.8%: 6.5 points higher than here.

The newest figure, in 2023, counts only 1 test (100.0% at or above 4 pCi/L), too few to compare, so this reading uses the 37-test figure.

Among its state's counties it ranks 51st of 72 Missouri counties with 30 or more tests for the same period. Statewide for the same period, Atchison County reported the highest share (70.5%) and Vernon County the lowest (9.1%).

Below the action level, 21 tests (56.8%) came in under 2 pCi/L, against 41.2% statewide, and 7 tests (18.9%) fell between 2 and 4, against 27.9% statewide. The busiest year on file was 2014, with 2 tests reported; the quietest, 2023, had 1.

EPA's 1993 zone map puts Monroe County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.

Next door, the shares run from 17.9% in Randolph County to 40.7% in Marion County, with Macon County and Randolph County below Monroe County.

Monroe County against Missouri, the United States and nearby counties, 2007 to 2016, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Monroe County
Monroe County3724.3%1.7 pCi/LThis county
Missouri, pooled115 counties, pooled54,94630.8%Not pooled+6.5 points
United States, pooled2,666 counties, pooled1,939,02535.8%Not pooled+11.5 points
Atchison Countyhighest in the state8870.5%5.5 pCi/L+46.2 points
Vernon Countylowest in the state339.1%1.2 pCi/L−15.2 points
Marion County, MOborders it27340.7%3.1 pCi/L+16.4 points
Ralls County, MOborders it5234.6%2.7 pCi/L+10.3 points
Audrain County, MOborders it12429.8%2.3 pCi/L+5.5 points
Shelby County, MOborders it2821.4%1.6 pCi/L−2.9 points
Macon County, MOborders it3619.4%1.7 pCi/L−4.9 points
Randolph County, MOborders it5617.9%1.7 pCi/L−6.4 points
Where Monroe County's reported results fell, 2007 to 2016, laboratory, beside Missouri and the United States
ResultMonroe County testsMonroe County shareMissouri shareU.S. shareAgainst Missouri
Under 2 pCi/L2156.8%41.2%39.6%+15.6 points
2 to 4 pCi/L718.9%27.9%24.6%−9.0 points
4 pCi/L and above924.3%30.8%35.8%−6.5 points
Monroe County ranked among the 72 Missouri counties with 30 or more tests, by share at or above 4 pCi/L, 2007 to 2016, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
St. Charles County46 of 726,28726.2%2.2 pCi/L
Moniteau County47 of 727025.7%2.3 pCi/L
Cole County48 of 7279025.7%2.2 pCi/L
Johnson County49 of 7226025.4%1.9 pCi/L
Texas County50 of 725625.0%1.4 pCi/L
Monroe County51 of 723724.3%1.7 pCi/L
Washington County51 of 723724.3%1.5 pCi/L
Morgan County53 of 7211323.9%2.3 pCi/L
Adair County54 of 728823.9%1.6 pCi/L
Lawrence County55 of 726823.5%1.7 pCi/L
Camden County56 of 7270522.8%2.2 pCi/L
Monroe County radon tests by year, against Missouri's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMissouri, pooledChange from the row before
20231100.0%6.7 pCi/L6.7 pCi/L35.7%+100.0 points
202220.0%1.6 pCi/L2.6 pCi/L40.8%Level
202010.0%2.3 pCi/L2.3 pCi/L33.2%Level
201920.0%0.9 pCi/L1.1 pCi/L33.5%−100.0 points
20181100.0%21.1 pCi/L21.1 pCi/L42.1%+100.0 points
201620.0%1.9 pCi/L2.6 pCi/L29.8%Level
201520.0%1.4 pCi/L1.6 pCi/L27.6%−100.0 points
20142100.0%4.5 pCi/L4.7 pCi/L34.4%First on file

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

Monroe County, Geology

The ground under Monroe County

Predicted

USGS's geologic map puts all of Monroe County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Dissected Till Plains, to which USGS gives a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under Monroe County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Dissected Till PlainsTill-covered Pennsylvanian sandstone, shale, and limestone.Moderate11100%

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

Monroe County beside the ground around it

Across Missouri 8.2% of the land is rated high; none of Monroe County's is. Of the 6 counties that border it, 1 has more high-potential ground, Marion County the most at 1.5%.

Share of land by USGS radon potential: Monroe County, the 6 counties bordering it and Missouri
AreaEPA zoneLow potentialModerate potentialHigh potential
Monroe CountyZone 2None100%None
Shelby CountyZone 2None100%None
Audrain CountyZone 2None100%None
Ralls CountyZone 2None100%None
Randolph CountyZone 2None100%None
Marion CountyZone 2None98.5%1.5%
Macon CountyZone 2None100%None
Missouri115 counties, pooled by land areaVaries5.8%86.0%8.2%

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

Local help

Monroe County, Local resources

Radon testing and mitigation in Monroe County

What Missouri's program says
Phone
573-751-6102
Email
radon@health.mo.gov

What it means

Monroe County, Questions

Questions about radon in Monroe County

Are radon levels high in Monroe County?

In 2023, 100.0% of the radon tests reported to CDC for Monroe County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.7 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 50 reported a higher share; pooled, the state comes to 30.8%.

Which counties border Monroe County?

Monroe County borders 6 counties: Shelby County, Audrain County, Ralls County, Randolph County, Marion County and Macon County.

Products

Monroe County, Products

Testing a home in Monroe County

In Monroe County, 24.3% of 37 tests reported to CDC over the 2007 to 2016 laboratory totals reached 4 pCi/L, against 30.8% pooled across Missouri. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Monroe County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Monroe County homes, compared

Explore

Monroe County, Bordering counties

Counties bordering Monroe County

Calculated by Radon411

Monroe County, Cities and towns

Cities and towns in Monroe County

The Census Bureau estimates 8,959 residents in Monroe County for July 1, 2025, 267 more than in 2020 (+3.1%). That works out to 14 people per square mile of land. Monroe City, the largest place on its list (2,714 residents in all), extends beyond Monroe County, so no share of the total is worked out for it. Reported testing is thin here: 37 tests over 2007 to 2016, or 4.1 for every 1,000 residents (2025 estimate), where Missouri as a whole comes to 8.8.

From Monroe City to Stoutsville, CDC publishes no figure by town: each reads Monroe County's.

The cities and towns in Monroe County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Monroe Cityextends beyond Monroe County2,714+2.0%Counted whole
Paris1,178+2.0%13.1%
Madison535+2.7%6.0%
Holliday119+4.4%1.3%
Stoutsville39+5.4%0.4%

5 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 Monroe County is counted whole, so it has no share.

Monroe County, Homes

Homes in Monroe County

Of Monroe County's 4,476 homes, 74% are detached houses, against 70% across Missouri; 19% are mobile homes. Half of its homes were built before 1977, close to Missouri's 1978: 31% date from before 1960 and 20% from 2000 or later. Owners live in 75% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.

Homes in Monroe County, Missouri, 2019 to 2023
HomesMonroe CountyMissouri
Housing units4,4762,809,501
Detached houses74%70%
In buildings of 5 or more3%13%
Mobile homes19%5%
Built before 196031%28%
Built since 200020%21%
Middle year built19771978
Owner-occupied75%68%

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