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Radon Levels in Knox County, Tennessee

EPA puts Knox County in Zone 1, its highest radon zone, and 17.7% of its 203 reported radon tests (2023) were 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

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  • Share at 4+ pCi/L

    17.7%

    7.2 pts below TN

    Knox
    17.7%
    Tennessee
    24.9%

    203 tests, 2023

  • Median result

    1.8pCi/L

    Below action level

    Knox
    1.8 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    203

    3rd of 15 by tests

    Knox
    203
    Hamblen
    594

    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 Tennessee

    10 of 15

    Middle half

    Knox
    17.7%
    Blount
    50.0%

    By share, of 15 with 30+ tests

Read a result for Knox County

Starts at Knox County's median, 1.8 pCi/L

1.8pCi/L

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

EPA’s reading of 1.8 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. Knox County's median reported result, 2023.

Interpret this reading

The data

Knox County, At a glance

Knox County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Knox 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 Knox County, 2023

Share of reported tests at or above 4 pCi/L, by year, Knox County
Share of reported tests at or above 4 pCi/L, by year, Knox County
YearShare of reported tests at or above 4 pCi/L
202214.1%
202317.7%

2023: 17.7%. Across these years the share ran from 14.1% to 17.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 203 tests reported to CDC for Knox 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

Knox County, Compared

Knox County radon figures, compared

Calculated by Radon411

Knox County's 203 reported tests in 2023 had a middle value of 1.8 pCi/L and a maximum of 18.2 pCi/L, and 17.7% reached 4 pCi/L. Tennessee as a whole (70 Tennessee counties, pooled) comes to 24.9%: 7.2 points higher than here.

Among its state's counties it ranks 10th of 15 Tennessee counties with 30 or more tests for the same period. Statewide for the same period, Blount County reported the highest share (50.0%) and Hamilton County the lowest (2.4%).

Below the action level, 114 tests (56.2%) came in under 2 pCi/L, against 49.4% statewide, and 53 tests (26.1%) fell between 2 and 4, against 25.7% statewide. The busiest year on file was 2022, with 1,599 tests reported; the quietest, 2023, had 203.

EPA's 1993 zone map puts Knox County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.

Next door, the shares run from 16.2% in Anderson County to 50.0% in Blount County, with Jefferson County and Anderson County below Knox County.

CDC also counts 45 tests taken after mitigation in Knox County for the same period: tests in homes where a fix was already in.

Knox County against Tennessee, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Knox County
Knox County20317.7%1.8 pCi/LThis county
Tennessee, pooled70 counties, pooled2,37824.9%Not pooled+7.2 points
United States, pooled642 counties, pooled128,74033.4%Not pooled+15.7 points
Hamblen Countyhighest in the state59437.0%3.1 pCi/L+19.3 points
Hamilton Countylowest in the state1692.4%0.7 pCi/L−15.3 points
Grainger County, TNborders it4100.0%12.5 pCi/L+82.3 points
Blount County, TNborders it4650.0%3.9 pCi/L+32.3 points
Loudon County, TNborders it8240.2%3.0 pCi/L+22.5 points
Sevier County, TNborders it1833.3%2.3 pCi/L+15.6 points
Union County, TNborders it333.3%1.8 pCi/L+15.6 points
Roane County, TNborders it2020.0%2.2 pCi/L+2.3 points
Jefferson County, TNborders it3517.1%2.6 pCi/L−0.6 points
Anderson County, TNborders it3716.2%1.4 pCi/L−1.5 points
Where Knox County's reported results fell, 2023, beside Tennessee and the United States
ResultKnox County testsKnox County shareTennessee shareU.S. shareAgainst Tennessee
Under 2 pCi/L11456.2%49.4%41.4%+6.8 points
2 to 4 pCi/L5326.1%25.7%25.2%+0.4 points
4 pCi/L and above3617.7%24.9%33.4%−7.2 points
Knox County ranked among the 15 Tennessee counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
Washington County5 of 154626.1%2.3 pCi/L
Bradley County6 of 1510525.7%2.2 pCi/L
Rutherford County7 of 155020.0%1.6 pCi/L
Sumner County7 of 153020.0%1.4 pCi/L
Cocke County9 of 1534718.4%1.4 pCi/L
Knox County10 of 1520317.7%1.8 pCi/L
Jefferson County11 of 153517.1%2.6 pCi/L
Williamson County12 of 1511516.5%1.3 pCi/L
Anderson County13 of 153716.2%1.4 pCi/L
Wilson County14 of 15822.4%0.9 pCi/L
Hamilton County15 of 151692.4%0.7 pCi/L
Knox County radon tests by year, against Tennessee's pooled share
YearTestsAt or above 4 pCi/LMedianHighestTennessee, pooledChange from the row before
202320317.7%1.8 pCi/L18.2 pCi/L24.9%+3.6 points
20221,59914.1%1.2 pCi/L48.8 pCi/L23.8%First on file

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

Knox County, Geology

The ground under Knox County

Predicted

USGS's geologic map puts all of Knox County's mapped land in one class: high radon potential. All of it lies in the area the map calls Ridge and Valley, to which USGS gives a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Knox County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Ridge and ValleyPaleozoic sandstone and cherty dolostone.High14100%

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

Knox County beside the ground around it

Knox County has more high-potential ground than Tennessee as a whole: 100% of its land against 47.2%. Of the 8 counties that border it, none has as large a share of high-potential ground; Grainger County comes nearest at 100%.

Share of land by USGS radon potential: Knox County, the 8 counties bordering it and Tennessee
AreaEPA zoneLow potentialModerate potentialHigh potential
Knox CountyZone 1NoneNone100%
Anderson CountyZone 131.4%None68.6%
Blount CountyZone 1None36.8%63.2%
Union CountyZone 1NoneNone100%
Sevier CountyZone 2None61.5%38.5%
Jefferson CountyZone 1NoneNone100%
Grainger CountyZone 1NoneNone100%
Loudon CountyZone 1NoneNone100%
Roane CountyZone 12.7%None97.3%
Tennessee95 counties, pooled by land areaVaries30.5%22.3%47.2%

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

Local help

Knox County, Local resources

Radon testing and mitigation in Knox County

What Tennessee's program says
Phone
1-800-232-1139
Email
TDEC.Radon@tn.gov

What it means

Knox County, Questions

Questions about radon in Knox County

Are radon levels high in Knox County?

In 2023, 17.7% of the radon tests reported to CDC for Knox County, Tennessee were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.8 pCi/L. Of 15 Tennessee counties with 30 or more tests for the same period, 9 reported a higher share; pooled, the state comes to 24.9%.

Which counties border Knox County?

Knox County borders 8 counties: Anderson County, Blount County, Union County, Sevier County, Jefferson County, Grainger County, Loudon County and Roane County.

Products

Knox County, Products

Testing a home in Knox County

In Knox County, 17.7% of 203 tests reported to CDC in 2023 reached 4 pCi/L, against 24.9% pooled across Tennessee. In Zone 1 the year-round level in Knox 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

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

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Knox County, Bordering counties

Counties bordering Knox County

Calculated by Radon411

Knox County, Cities and towns

Cities and towns in Knox County

Knox County is growing: the Census Bureau puts it at 511,453 residents on July 1, 2025, up 6.4% from 480,472 in 2020. Packed into its land, that is 1,006 people per square mile. Its largest town, Knoxville, has 202,021 residents, 39.5% of the total. CDC's 203 reported tests for 2023 work out to 0.4 per 1,000 residents (2025 estimate), close to Tennessee's 0.3.

From Knoxville to Farragut, CDC publishes no figure by town: each reads Knox County's.

The cities and towns in Knox County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Knoxville202,021+5.7%39.5%
Farragutextends beyond Knox County25,121+6.6%Counted whole

2 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 Knox County is counted whole, so it has no share.

Knox County, Homes

Homes in Knox County

Of Knox County's 214,606 homes, 66% are detached houses, against 68% across Tennessee; 20% are in buildings of five or more homes. Half of its homes were built before 1985, close to Tennessee's 1986: 20% date from before 1960 and 27% from 2000 or later. 65% of occupied homes are lived in by their owner (Tennessee: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Knox County, Tennessee, 2019 to 2023
HomesKnox CountyTennessee
Housing units214,6063,095,472
Detached houses66%68%
In buildings of 5 or more20%14%
Mobile homes4%8%
Built before 196020%18%
Built since 200027%29%
Middle year built19851986
Owner-occupied65%67%

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