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Radon Levels in Webster County, Missouri

EPA puts Webster County 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

    20.4%

    10.2 pts below MO

    Webster
    20.4%
    Missouri
    30.6%

    103 tests, 2008 to 2017

  • Median result

    1.6pCi/L

    Below action level

    Webster
    1.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    103

    40th of 72 by tests

    Webster
    103
    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

    59 of 72

    Lowest quarter

    Webster
    20.4%
    Atchison
    69.9%

    By share, of 72 with 30+ tests

Read a result for Webster County

Starts at Webster County's median, 1.6 pCi/L

1.6pCi/L

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

EPA’s reading of 1.6 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. Webster County's median reported result, 2008 to 2017.

Interpret this reading

The data

Webster County, At a glance

Webster County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Webster 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 Webster County, 2023

Share of reported tests at or above 4 pCi/L, by year, Webster County
Share of reported tests at or above 4 pCi/L, by year, Webster County
YearShare of reported tests at or above 4 pCi/L
201425.0%
20150.0%
201625.0%
20170.0%
20180.0%
20190.0%
202020.0%
20210.0%
202231.3%
202311.1%

2023: 11.1%. Across these years the share ran from 0.0% to 31.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 9 tests were reported to CDC for Webster 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

Webster County, Compared

Webster County radon figures, compared

Calculated by Radon411

Webster County's 103 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.6 pCi/L and a maximum of 20.9 pCi/L, and 20.4% reached 4 pCi/L. Missouri as a whole (115 Missouri counties, pooled) comes to 30.6%: 10.2 points higher than here.

The newest figure, in 2023, counts only 9 tests (11.1% at or above 4 pCi/L), too few to compare, so this reading uses the 103-test figure.

Among its state's counties it ranks 59th 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, 61 tests (59.2%) came in under 2 pCi/L, against 41.2% statewide, and 21 tests (20.4%) fell between 2 and 4, against 28.1% statewide. The busiest year on file was 2022, with 16 tests reported; the quietest, 2021, had 2.

EPA's 1993 zone map puts Webster 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 31.7% in Christian County to 37.0% in Laclede County.

Webster County against Missouri, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Webster County
Webster County10320.4%1.6 pCi/LThis county
Missouri, pooled115 counties, pooled58,52530.6%Not pooled+10.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+15.3 points
Atchison Countyhighest in the state10369.9%5.6 pCi/L+49.5 points
Vernon Countylowest in the state348.8%0.9 pCi/L−11.6 points
Laclede County, MOborders it4637.0%2.3 pCi/L+16.6 points
Greene County, MOborders it1,47032.7%2.5 pCi/L+12.3 points
Christian County, MOborders it43631.7%1.9 pCi/L+11.3 points
Wright County, MOborders it1827.8%2.7 pCi/L+7.4 points
Dallas County, MOborders it2714.8%1.4 pCi/L−5.6 points
Douglas County, MOborders it30.0%1.2 pCi/L−20.4 points
Where Webster County's reported results fell, 2008 to 2017, laboratory, beside Missouri and the United States
ResultWebster County testsWebster County shareMissouri shareU.S. shareAgainst Missouri
Under 2 pCi/L6159.2%41.2%39.6%+18.0 points
2 to 4 pCi/L2120.4%28.1%24.7%−7.7 points
4 pCi/L and above2120.4%30.6%35.7%−10.2 points
Webster County 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
Camden County54 of 7276322.9%2.2 pCi/L
Livingston County55 of 724922.4%2.1 pCi/L
Boone County56 of 724,76721.7%1.9 pCi/L
Butler County57 of 723321.2%1.9 pCi/L
Morgan County58 of 7212321.1%2.2 pCi/L
Webster County59 of 7210320.4%1.6 pCi/L
Macon County60 of 723619.4%1.7 pCi/L
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
Webster County radon tests by year, against Missouri's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMissouri, pooledChange from the row before
2023911.1%0.7 pCi/L17.0 pCi/L35.7%−20.2 points
20221631.3%2.0 pCi/L21.0 pCi/L40.8%+31.3 points
202120.0%0.6 pCi/L0.9 pCi/L31.8%−20.0 points
20201020.0%2.0 pCi/L9.7 pCi/L33.2%+20.0 points
201920.0%1.8 pCi/L1.9 pCi/L33.5%Level
201830.0%2.1 pCi/L3.1 pCi/L42.1%Level
201720.0%1.2 pCi/L2.1 pCi/L37.0%−25.0 points
2016425.0%2.2 pCi/L6.1 pCi/L29.8%+25.0 points
201550.0%1.3 pCi/L2.1 pCi/L27.6%−25.0 points
2014825.0%1.6 pCi/L10.1 pCi/L34.4%First on file

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

Webster County, Geology

The ground under Webster County

Predicted

USGS's geologic map puts all of Webster County's mapped land in one class: moderate radon potential. The map puts 73.2% of Webster County in the area it calls Salem Plateau and 26.8% in Springfield Plateau. USGS gives both a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under Webster County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Salem PlateauOrdovician dolomite, sandstone, limestone, and shale.Moderate1173.2%
Springfield PlateauMississippian limestone, shale, and sandstone.Moderate1126.8%

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

Webster County beside the ground around it

Across Missouri 8.2% of the land is rated high; none of Webster County's is. Of the 6 counties that border it, none has as large a share of moderate-potential ground; Christian County comes nearest at 100%.

Share of land by USGS radon potential: Webster County, the 6 counties bordering it and Missouri
AreaEPA zoneLow potentialModerate potentialHigh potential
Webster CountyZone 2None100%None
Dallas CountyZone 2None100%None
Wright CountyZone 2None100%None
Greene CountyZone 2None100%None
Laclede CountyZone 2None100%None
Christian CountyZone 2None100%None
Douglas 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

Webster County, Local resources

Radon testing and mitigation in Webster County

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

What it means

Webster County, Questions

Questions about radon in Webster County

Are radon levels high in Webster County?

In 2023, 11.1% of the radon tests reported to CDC for Webster County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.7 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 58 reported a higher share; pooled, the state comes to 30.6%.

Which counties border Webster County?

Webster County borders 6 counties: Dallas County, Wright County, Greene County, Laclede County, Christian County and Douglas County.

Products

Webster County, Products

Testing a home in Webster County

In Webster County, 20.4% of 103 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 Webster County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Webster County homes, compared

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Webster County, Bordering counties

Counties bordering Webster County

Calculated by Radon411

Webster County, Cities and towns

Cities and towns in Webster County

Webster County is growing: the Census Bureau puts it at 43,054 residents on July 1, 2025, up 10.4% from 39,012 in 2020. That works out to 73 people per square mile of land. No town dominates: Marshfield, the largest, has 8,078 residents, 18.8% of the total. Reported testing is thin here: 103 tests over 2008 to 2017, or 2.4 for every 1,000 residents (2025 estimate), where Missouri as a whole comes to 9.3.

From Marshfield to Diggins, CDC publishes no figure by town: each reads Webster County's.

The cities and towns in Webster County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Marshfield8,078+7.8%18.8%
Rogersvilleextends beyond Webster County5,754+47.7%Counted whole
Straffordextends beyond Webster County2,789+8.5%Counted whole
Seymour1,960+6.2%4.6%
Fordland824+6.0%1.9%
Niangua425+6.8%1.0%
Diggins319+5.6%0.7%

7 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 Webster County is counted whole, so it has no share.

Webster County, Homes

Homes in Webster County

Webster County is a place of houses on their own lots: 78% of its 15,360 homes are detached single-family houses, against 70% across Missouri. Much of Webster County is recent building: 31% of its homes have gone up since 2000 and the middle year built is 1990, against 1978 for Missouri. Owners live in 77% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.

Homes in Webster County, Missouri, 2019 to 2023
HomesWebster CountyMissouri
Housing units15,3602,809,501
Detached houses78%70%
In buildings of 5 or more3%13%
Mobile homes11%5%
Built before 196015%28%
Built since 200031%21%
Middle year built19901978
Owner-occupied77%68%

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