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Radon Levels in St. Louis city, Missouri

EPA puts St. Louis city in Zone 2, its middle radon zone, and only 9 radon tests from it are 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

    16.9%

    13.7 pts below MO

    St. Louis city
    16.9%
    Missouri
    30.6%

    1,873 tests, 2008 to 2017

  • Median result

    1.9pCi/L

    Below action level

    St. Louis city
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,873

    7th of 72 by tests

    St. Louis city
    1,873
    St. Louis
    17,747

    Reported to CDC before any fix, 2008 to 2017

  • 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

    66 of 72

    Lowest quarter

    St. Louis city
    16.9%
    Atchison
    69.9%

    By share, of 72 with 30+ tests

Read a result for St. Louis city

Starts at St. Louis city's median, 1.9 pCi/L

1.9pCi/L

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

EPA’s reading of 1.9 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. St. Louis city's median reported result, 2008 to 2017.

Interpret this reading

The data

St. Louis city, At a glance

St. Louis city at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

St. Louis city 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 St. Louis city, 2023

Share of reported tests at or above 4 pCi/L, by year, St. Louis city
Share of reported tests at or above 4 pCi/L, by year, St. Louis city
YearShare of reported tests at or above 4 pCi/L
201418.7%
201511.5%
201615.3%
201725.6%
201813.8%
201925.0%
202010.0%
202117.6%
202219.8%
202333.3%

2023: 33.3%. Across these years the share ran from 10.0% to 33.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 9 tests were reported to CDC for St. Louis city 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

St. Louis city, Compared

St. Louis city radon figures, compared

Calculated by Radon411

St. Louis city's 1,873 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.9 pCi/L and a maximum of 67.3 pCi/L, and 16.9% reached 4 pCi/L. Missouri as a whole (115 Missouri counties, pooled) comes to 30.6%: 13.7 points higher than here.

The newest figure, in 2023, counts only 9 tests (33.3% at or above 4 pCi/L), too few to compare, so this reading uses the 1,873-test figure.

Among its state's counties it ranks 66th of 72 Missouri counties with 30 or more tests for the same period. Statewide for the same period, Atchison County reported the highest share (69.9%) and Vernon County the lowest (8.8%).

Below the action level, 958 tests (51.1%) came in under 2 pCi/L, against 41.2% statewide, and 599 tests (32.0%) fell between 2 and 4, against 28.1% statewide. The busiest year on file was 2022, with 192 tests reported; the quietest, 2023, had 9.

EPA's 1993 zone map puts St. Louis city 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 26.3% in St. Louis County to 44.2% in St. Clair County, IL. Over 7 years of annual figures the share held within 2 points, from 18.7% in 2014 to 19.8% in 2022; its peak was 25.6% in 2017.

CDC also counts 24 tests taken after mitigation in St. Louis city for the same period: tests in homes where a fix was already in.

Share of reported tests at or above 4 pCi/L by year, St. Louis city against Missouri2014 to 2022, years with 30 or more tests: St. Louis city 18.7% to 19.8%, the state's pooled share 40.8% in 2022.
St. Louis cityMissouri, pooled
Share of reported tests at or above 4 pCi/L by year, St. Louis city against Missouri: data table
YearTestsSt. Louis city, at or above 4 pCi/LMissouri, pooled
201410718.7%34.4%
201513911.5%27.6%
201614415.3%29.8%
20178225.6%37.0%
20194825.0%33.5%
202111917.6%31.8%
202219219.8%40.8%
St. Louis city against Missouri, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from St. Louis city
St. Louis city1,87316.9%1.9 pCi/LThis county
Missouri, pooled115 counties, pooled58,52530.6%Not pooled+13.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+18.8 points
Atchison Countyhighest in the state10369.9%5.6 pCi/L+53.0 points
Vernon Countylowest in the state348.8%0.9 pCi/L−8.1 points
St. Clair County, ILborders it2,77144.2%3.5 pCi/L+27.3 points
Madison County, ILborders it3,34337.4%3.0 pCi/L+20.5 points
St. Louis County, MOborders it17,74726.3%2.3 pCi/L+9.4 points
Where St. Louis city's reported results fell, 2008 to 2017, laboratory, beside Missouri and the United States
ResultSt. Louis city testsSt. Louis city shareMissouri shareU.S. shareAgainst Missouri
Under 2 pCi/L95851.1%41.2%39.6%+9.9 points
2 to 4 pCi/L59932.0%28.1%24.7%+3.9 points
4 pCi/L and above31616.9%30.6%35.7%−13.7 points
St. Louis city ranked among the 72 Missouri counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Texas County61 of 725719.3%1.3 pCi/L
Linn County62 of 723718.9%1.8 pCi/L
Pulaski County63 of 7210718.7%1.3 pCi/L
Randolph County64 of 725817.2%1.8 pCi/L
Miller County65 of 7215416.9%1.9 pCi/L
St. Louis city66 of 721,87316.9%1.9 pCi/L
Osage County67 of 725215.4%1.5 pCi/L
Phelps County68 of 7220414.7%1.5 pCi/L
Crawford County68 of 723414.7%1.5 pCi/L
Montgomery County70 of 724712.8%1.6 pCi/L
Polk County71 of 727811.5%1.6 pCi/L
St. Louis city radon tests by year, against Missouri's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMissouri, pooledChange from the row before
2023933.3%1.7 pCi/L16.7 pCi/L35.7%+13.5 points
202219219.8%2.0 pCi/L15.5 pCi/L40.8%+2.2 points
202111917.6%1.7 pCi/L19.5 pCi/L31.8%+7.6 points
20202010.0%1.6 pCi/L17.0 pCi/L33.2%−15.0 points
20194825.0%1.9 pCi/L16.8 pCi/L33.5%+11.2 points
20182913.8%2.8 pCi/L7.4 pCi/L42.1%−11.8 points
20178225.6%2.1 pCi/L22.7 pCi/L37.0%+10.3 points
201614415.3%1.7 pCi/L67.3 pCi/L29.8%+3.8 points
201513911.5%2.0 pCi/L11.9 pCi/L27.6%−7.2 points
201410718.7%2.1 pCi/L20.2 pCi/L34.4%First on file

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

St. Louis city, Geology

The ground under St. Louis city

Predicted

USGS's geologic map puts all of St. Louis city's mapped land in one class: moderate radon potential. 98.5% of it lies in the area the map calls Salem Plateau, to which USGS gives a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under St. Louis city
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Salem PlateauOrdovician dolomite, sandstone, limestone, and shale.Moderate1198.5%
Southern Central Lowland ProvinceIllinoian glacial deposits, sandstone, and gray shale.Moderate91.4%

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

St. Louis city beside the ground around it

Across Missouri 8.2% of the land is rated high; none of St. Louis city's is. Of the 3 counties that border it, 1 has more high-potential ground, Madison County, IL the most at 8.3%.

Share of land by USGS radon potential: St. Louis city, the 3 counties bordering it and Missouri
AreaEPA zoneLow potentialModerate potentialHigh potential
St. Louis cityZone 2None100%None
St. Louis CountyZone 2None100%None
St. Clair County, ILZone 2None100%None
Madison County, ILZone 2None91.7%8.3%
Missouri115 counties, pooled by land areaVaries5.8%86.0%8.2%

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

Local help

St. Louis city, Local resources

Radon testing and mitigation in St. Louis city

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

What it means

St. Louis city, Questions

Questions about radon in St. Louis city

Are radon levels high in St. Louis city?

In 2023, 33.3% of the radon tests reported to CDC for St. Louis city, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.7 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 65 reported a higher share; pooled, the state comes to 30.6%.

Which counties border St. Louis city?

St. Louis city borders 3 counties: St. Louis County, MO, St. Clair County, IL and Madison County, IL.

Products

St. Louis city, Products

Testing a home in St. Louis city

In St. Louis city, 16.9% of 1,873 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 30.6% pooled across Missouri. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in St. Louis city; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for St. Louis city homes, compared

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St. Louis city, Bordering counties

Counties bordering St. Louis city

Calculated by Radon411

St. Louis city, Cities and towns

Cities and towns in St. Louis city

St. Louis city has been losing residents: from 300,302 in 2020 to 278,144 on July 1, 2025, a fall of 7.4% by the Census Bureau's estimates. Packed into its land, that is 4,505 people per square mile. St. Louis, its one incorporated place, has 278,144 residents, 100.0% of the total. CDC's 1,873 reported tests for 2008 to 2017 work out to 6.7 per 1,000 residents (2025 estimate), close to Missouri's 9.3.

St. Louis is the one incorporated place here; CDC publishes no figure by town, so it reads St. Louis city's.

St. Louis, St. Louis city: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
St. Louis278,144−7.4%100.0%

One incorporated place, 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).

St. Louis city, Homes

Homes in St. Louis city

Fewer than six in ten of St. Louis city's 173,920 homes are detached houses (43%, against 70% across Missouri); the rest are attached, in shared buildings or mobile. More than half of its homes were built before 1940, where the middle year for Missouri is 1978; 7% have gone up since 2000. Most occupied homes here are rented: owners live in 45% (Missouri: 68%). A tenant can run a test; a fix is the landlord's to make.

Homes in St. Louis city, Missouri, 2019 to 2023
HomesSt. Louis cityMissouri
Housing units173,9202,809,501
Detached houses43%70%
In buildings of 5 or more25%13%
Mobile homesunder 1%5%
Built before 196075%28%
Built since 20007%21%
Middle year built1939 or earlier1978
Owner-occupied45%68%

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