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Radon Levels in Clay County, Missouri

EPA puts Clay County in Zone 1, its highest radon zone, and high results are common there: 44.6% of the 83 radon tests reported to CDC (2023) 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

    44.6%

    8.9 pts above MO

    Clay
    44.6%
    Missouri
    35.7%

    83 tests, 2023

  • Median result

    3.6pCi/L

    Below action level

    Clay
    3.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    83

    4th of 7 by tests

    Clay
    83
    St. Louis
    443

    Reported to CDC before any fix, 2023

  • 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 Missouri

    1 of 7

    Top quarter

    Clay
    44.6%
    Clay
    44.6%

    By share, of 7 with 30+ tests

Read a result for Clay County

Starts at Clay County's median, 3.6 pCi/L

3.6pCi/L

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

EPA’s reading of 3.6 pCi/L

Between 2 and 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 between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Clay County's median reported result, 2023.

Interpret this readingWhat a fix costs

The data

Clay County, At a glance

Clay County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Clay 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 73% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Clay County, 2023

Share of reported tests at or above 4 pCi/L, by year, Clay County
Share of reported tests at or above 4 pCi/L, by year, Clay County
YearShare of reported tests at or above 4 pCi/L
201442.0%
201526.9%
201635.6%
201733.3%
201836.0%
201924.1%
202048.1%
202140.0%
202251.4%
202344.6%

2023: 44.6%. Across these years the share ran from 24.1% to 51.4%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 83 tests reported to CDC for Clay County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Clay County, Compared

Clay County radon figures, compared

Calculated by Radon411

In Clay County, about 4 in 10 reported tests in 2023 (37 of 83) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 11.2 points higher. Across 91 Missouri counties pooled together, 35.7% of tests reached that level, so Clay County runs 8.9 points above its state.

Jackson County, the one bordering county with a figure for the same period, reported 44.1%. By share, Clay County is 1st of 7 Missouri counties with 30 or more tests for the same period.

Year by year, 2014 opened at 42.0% and 2023 closed at 44.6% (up 2.6 points), with 2022 the high at 51.4%. Half the tests came in under 3.6 pCi/L and half over it; the single highest reached 61.2 pCi/L. Below the action level, 23 tests (27.7%) came in under 2 pCi/L, against 36.6% statewide, and 23 tests (27.7%) fell between 2 and 4, against 27.7% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 44.6% share point the same way here. USGS geology rates 73% of the county's land high radon potential.

The busiest year on file was 2016, with 222 tests reported; the quietest, 2020, had 54.

Share of reported tests at or above 4 pCi/L by year, Clay County against Missouri2014 to 2023, years with 30 or more tests: Clay County 42.0% to 44.6%, the state's pooled share 35.7% in 2023.
Clay CountyMissouri, pooled
Share of reported tests at or above 4 pCi/L by year, Clay County against Missouri: data table
YearTestsClay County, at or above 4 pCi/LMissouri, pooled
201420542.0%34.4%
201513026.9%27.6%
201622235.6%29.8%
201715933.3%37.0%
20188636.0%42.1%
20195424.1%33.5%
20205448.1%33.2%
20216540.0%31.8%
202211151.4%40.8%
20238344.6%35.7%
Clay County against Missouri, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Clay County
Clay County8344.6%3.6 pCi/LThis county
Missouri, pooled91 counties, pooled1,41235.7%Not pooled−8.9 points
United States, pooled642 counties, pooled128,74033.4%Not pooled−11.2 points
Boone Countyhighest in the state6342.9%3.6 pCi/L−1.7 points
St. Louis Countylowest in the state44322.6%2.0 pCi/L−22.0 points
Jackson County, MOborders it20444.1%3.4 pCi/L−0.5 points
Platte County, MOborders it2937.9%3.0 pCi/L−6.7 points
Ray County, MOborders it728.6%2.0 pCi/L−16.0 points
Where Clay County's reported results fell, 2023, beside Missouri and the United States
ResultClay County testsClay County shareMissouri shareU.S. shareAgainst Missouri
Under 2 pCi/L2327.7%36.6%41.4%−8.9 points
2 to 4 pCi/L2327.7%27.7%25.2%Level
4 pCi/L and above3744.6%35.7%33.4%+8.9 points
Clay County ranked among the 7 Missouri counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
Clay County1 of 78344.6%3.6 pCi/L
Jackson County2 of 720444.1%3.4 pCi/L
Boone County3 of 76342.9%3.6 pCi/L
St. Charles County4 of 710340.8%3.4 pCi/L
Jefferson County5 of 73638.9%3.4 pCi/L
Greene County6 of 74827.1%2.9 pCi/L
St. Louis County7 of 744322.6%2.0 pCi/L
Clay County radon tests by year, against Missouri's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMissouri, pooledChange from the row before
20238344.6%3.6 pCi/L61.2 pCi/L35.7%−6.8 points
202211151.4%4.2 pCi/L32.3 pCi/L40.8%+11.4 points
20216540.0%2.8 pCi/L29.2 pCi/L31.8%−8.1 points
20205448.1%3.8 pCi/L21.9 pCi/L33.2%+24.0 points
20195424.1%2.4 pCi/L11.1 pCi/L33.5%−11.9 points
20188636.0%3.1 pCi/L21.3 pCi/L42.1%+2.7 points
201715933.3%2.4 pCi/L27.3 pCi/L37.0%−2.3 points
201622235.6%3.0 pCi/L29.9 pCi/L29.8%+8.7 points
201513026.9%2.2 pCi/L16.9 pCi/L27.6%−15.1 points
201420542.0%3.2 pCi/L65.0 pCi/L34.4%First on file

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

Clay County, Geology

The ground under Clay County

Predicted

USGS's geologic map splits Clay County: 72.6% of its land is high radon potential and 27.4% moderate. The map puts 72.6% of Clay County in the area it calls Northwestern Dissected Till Plains and 27.1% in Dissected Till Plains. USGS gives the first a radon index of 13, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Clay County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Northwestern Dissected Till PlainsPennsylvanian shales covered by thick loess.High1372.6%
Dissected Till PlainsTill-covered Pennsylvanian sandstone, shale, and limestone.Moderate1127.1%

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

Clay County beside the ground around it

Clay County has more high-potential ground than Missouri as a whole: 72.6% of its land against 8.2%. Of the 5 counties that border it, 2 have more high-potential ground, Platte County the most at 100%.

Share of land by USGS radon potential: Clay County, the 5 counties bordering it and Missouri
AreaEPA zoneLow potentialModerate potentialHigh potential
Clay CountyZone 1None27.4%72.6%
Platte CountyZone 1NoneNone100%
Clinton CountyZone 1None32.8%67.2%
Ray CountyZone 2None100%None
Jackson CountyZone 1None30.5%69.5%
Wyandotte County, KSZone 1NoneNone100%
Missouri115 counties, pooled by land areaVaries5.8%86.0%8.2%

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

Local help

Clay County, Local resources

Radon testing and mitigation in Clay County

Listed radon businesses with an address in Clay County:

Listed radon professionals by town: Kansas City, Gladstone, Smithville

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

What it means

Clay County, Questions

Questions about radon in Clay County

Are radon levels high in Clay County?

In 2023, 44.6% of the radon tests reported to CDC for Clay County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.6 pCi/L. Of 7 Missouri counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 35.7%.

Which counties border Clay County?

Clay County borders 5 counties: Platte County, MO, Clinton County, MO, Ray County, MO, Jackson County, MO and Wyandotte County, KS.

Products

Clay County, Products

Testing a home in Clay County

In Clay County, 44.6% of 83 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Missouri. In Zone 1 the year-round level in Clay 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

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

Explore

Clay County, Bordering counties

Counties bordering Clay County

Calculated by Radon411

Clay County, Cities and towns

Cities and towns in Clay County

The Census Bureau estimates 265,032 residents in Clay County for July 1, 2025, 10,911 more than in 2020 (+4.3%). That works out to 666 people per square mile of land. Kansas City, the largest place on its list (521,220 residents in all), extends beyond Clay County, so no share of the total is worked out for it. CDC's 83 reported tests for 2023 work out to 0.3 per 1,000 residents (2025 estimate), close to Missouri's 0.2.

From Kansas City to Randolph, CDC publishes no figure by town: each reads Clay County's.

The 12 largest cities and towns in Clay County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Kansas Cityextends beyond Clay County521,220+2.6%Counted whole
Independenceextends beyond Clay County121,675−1.0%Counted whole
Liberty31,319+3.7%11.8%
Gladstone27,497+1.5%10.4%
Kearney11,296+7.9%4.3%
Smithvilleextends beyond Clay County11,160+6.5%Counted whole
Excelsior Springsextends beyond Clay County10,819+2.3%Counted whole
North Kansas City5,613+22.8%2.1%
Sugar Creekextends beyond Clay County3,209−2.7%Counted whole
Pleasant Valley2,747−0.2%1.0%
Lawsonextends beyond Clay County2,541+0.6%Counted whole
Claycomo1,362+1.5%0.5%
  • Glenaire
  • Holt (part)
  • Avondale
  • Oakview
  • Excelsior Estates (part)
  • Missouri City
  • Oakwood
  • Oakwood Park
  • Birmingham
  • Prathersville
  • Oaks
  • Mosby
  • Randolph

25 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Clay County is counted whole, so it has no share.

Clay County, Homes

Homes in Clay County

Of Clay County's 106,689 homes, 71% are detached houses, against 70% across Missouri; 17% are in buildings of five or more homes. Much of Clay County is recent building: 32% of its homes have gone up since 2000 and the middle year built is 1987, against 1978 for Missouri. 69% of occupied homes are lived in by their owner (Missouri: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Clay County, Missouri, 2019 to 2023
HomesClay CountyMissouri
Housing units106,6892,809,501
Detached houses71%70%
In buildings of 5 or more17%13%
Mobile homes2%5%
Built before 196018%28%
Built since 200032%21%
Middle year built19871978
Owner-occupied69%68%

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