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Radon Levels in Knox County, Indiana

EPA puts Knox County in Zone 2, its middle radon zone, and high results are common there: 43.1% of the 58 radon tests reported to CDC (2008 to 2017, laboratory totals) 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

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  • Share at 4+ pCi/L

    43.1%

    4.2 pts above IN

    Knox
    43.1%
    Indiana
    38.9%

    58 tests, 2008 to 2017

  • Median result

    3.4pCi/L

    Below action level

    Knox
    3.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    58

    60th of 69 by tests

    Knox
    58
    St. Joseph
    7,346

    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 Indiana

    35 of 69

    Middle half

    Knox
    43.1%
    Miami
    63.3%

    By share, of 69 with 30+ tests

Read a result for Knox County

Starts at Knox County's median, 3.4 pCi/L

3.4pCi/L

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

EPA’s reading of 3.4 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. Knox County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Knox County, At a glance

Knox County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Knox 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 Knox County, 2008 to 2017, laboratory

Reported results by concentration band, Knox County, 2008 to 2017, laboratory
Under 2 pCi/L: 24%2 to 4 pCi/L: 33%4 pCi/L and above: 43%

Of 58 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Knox County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L1424.1%
2 to 4 pCi/L1932.8%
4 pCi/L and above2543.1%
What these figures count

These are the 58 tests reported to CDC for Knox County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Knox County, Compared

Knox County radon figures, compared

Calculated by Radon411

In Knox County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (25 of 58) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 7.4 points higher. Across 92 Indiana counties pooled together, 38.9% of tests reached that level, so Knox County runs 4.2 points above its state.

Of 6 neighbours with a figure, 1 reported a larger share at or above 4 pCi/L and 5 a smaller one; the spread is 18.8% (Lawrence County, IL) to 43.3% (Gibson County). By share, Knox County is 35th of 69 Indiana counties with 30 or more tests for the same period.

Half the tests came in under 3.4 pCi/L and half over it; the single highest reached 12.1 pCi/L. Below the action level, 14 tests (24.1%) came in under 2 pCi/L, against 32.8% statewide, and 19 tests (32.8%) fell between 2 and 4, against 28.3% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 43.1% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential.

CDC's ten-year totals for Knox County went from 61 tests (2005 to 2014) to 58 (2008 to 2017), the share going from 45.9% to 43.1%.

Knox County against Indiana, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Knox County
Knox County5843.1%3.4 pCi/LThis county
Indiana, pooled92 counties, pooled43,14838.9%Not pooled−4.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−7.4 points
Miami Countyhighest in the state3063.3%5.3 pCi/L+20.2 points
Jasper Countylowest in the state7114.1%1.2 pCi/L−29.0 points
Pike County, INborders it650.0%3.6 pCi/L+6.9 points
Sullivan County, INborders it1346.2%3.1 pCi/L+3.1 points
Gibson County, INborders it12043.3%3.4 pCi/L+0.2 points
Daviess County, INborders it5834.5%3.1 pCi/L−8.6 points
Greene County, INborders it4932.7%3.0 pCi/L−10.4 points
Wabash County, ILborders it3432.4%3.0 pCi/L−10.7 points
Crawford County, ILborders it18119.3%1.8 pCi/L−23.8 points
Lawrence County, ILborders it4818.8%1.8 pCi/L−24.3 points
Where Knox County's reported results fell, 2008 to 2017, laboratory, beside Indiana and the United States
ResultKnox County testsKnox County shareIndiana shareU.S. shareAgainst Indiana
Under 2 pCi/L1424.1%32.8%39.6%−8.7 points
2 to 4 pCi/L1932.8%28.3%24.7%+4.5 points
4 pCi/L and above2543.1%38.9%35.7%+4.2 points
Knox County ranked among the 69 Indiana counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Morgan County30 of 6922644.2%3.5 pCi/L
Dubois County31 of 6913644.1%3.7 pCi/L
Vigo County32 of 6945544.0%3.6 pCi/L
Huntington County33 of 6916943.8%3.5 pCi/L
Gibson County34 of 6912043.3%3.4 pCi/L
Knox County35 of 695843.1%3.4 pCi/L
Floyd County36 of 6931642.4%3.3 pCi/L
Washington County37 of 693842.1%3.5 pCi/L
Allen County38 of 693,99041.8%3.3 pCi/L
LaGrange County39 of 6912041.7%3.4 pCi/L
Hendricks County40 of 691,17041.5%3.2 pCi/L
Knox County ten-year laboratory totals, against Indiana's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIndiana, pooledChange from the row before
2008 to 20175843.1%3.4 pCi/L12.1 pCi/L38.9%+1.3 points
2007 to 20165541.8%3.1 pCi/L18.5 pCi/L39.2%−3.4 points
2006 to 20156245.2%3.7 pCi/L18.5 pCi/L39.6%−0.7 points
2005 to 20146145.9%3.8 pCi/L18.5 pCi/L39.3%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: moderate radon potential. All of it lies in the area the map calls Wabash Lowland, to which USGS gives a radon index of 10, in the moderate band (9 to 11).

USGS's geologic areas under Knox County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Wabash LowlandLoess, pre-Wisconsinan glacial deposits, Pennsylvanian shale, sandstone, and carbonate bedrock.Moderate1099.7%

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

Across Indiana 56.6% of the land is rated high; none of Knox County's is. Of the 8 counties that border it, none has as large a share of moderate-potential ground; Daviess County comes nearest at 100%.

Share of land by USGS radon potential: Knox County, the 8 counties bordering it and Indiana
AreaEPA zoneLow potentialModerate potentialHigh potential
Knox CountyZone 2None100%None
Lawrence County, ILZone 2None100%None
Daviess CountyZone 2None100%None
Pike CountyZone 2None100%None
Gibson CountyZone 2None100%None
Wabash County, ILZone 2None100%None
Sullivan CountyZone 2None100%None
Crawford County, ILZone 2None100%None
Greene CountyZone 2None100%None
Indiana92 counties, pooled by land areaVariesNone43.4%56.6%

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 Indiana's program says
Phone
1-800-272-9723
Licensing of radon professionals
According to the Indiana Radon Rule, 410 IAC 5.1, everyone who is serving Indiana by doing radon testing, analysis and mitigation (radon reduction) in residential structures must be certified by the Indiana State Department of Health.

What it means

Knox County, Questions

Questions about radon in Knox County

Are radon levels high in Knox County?

Over the 2008 to 2017 laboratory totals, 43.1% of the radon tests reported to CDC for Knox County, Indiana were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.4 pCi/L. Of 69 Indiana counties with 30 or more tests for the same period, 34 reported a higher share; pooled, the state comes to 38.9%.

Which counties border Knox County?

Knox County borders 8 counties: Lawrence County, IL, Daviess County, IN, Pike County, IN, Gibson County, IN, Wabash County, IL, Sullivan County, IN, Crawford County, IL and Greene County, IN.

Products

Knox County, Products

Testing a home in Knox County

In Knox County, 43.1% of 58 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 38.9% pooled across Indiana. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Knox County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Knox County homes, compared

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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

About 35,652 people live in Knox County by the Census Bureau's estimate for July 1, 2025, 601 fewer than in 2020 (−1.7%). That works out to 69 people per square mile of land. Its largest town, Vincennes, has 16,378 residents, 45.9% of the total. Together its 9 incorporated places hold 62.0% of those residents; the other 38.0% live outside any of them. Reported testing is thin here: 58 tests over 2008 to 2017, or 1.6 for every 1,000 residents (2025 estimate), where Indiana as a whole comes to 6.2.

From Vincennes to Decker, 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
Vincennes16,378−2.3%45.9%
Bicknell2,982−1.7%8.4%
Oaktown576−0.3%1.6%
Monroe City487−1.0%1.4%
Bruceville448−0.4%1.3%
Wheatland391−0.5%1.1%
Sandborn359−0.8%1.0%
Edwardsport276−1.8%0.8%
Decker197−0.5%0.6%

9 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).

Knox County, Homes

Homes in Knox County

Of Knox County's 16,965 homes, 75% are detached houses, against 73% across Indiana; 8% are in buildings of five or more homes. The homes are older than Indiana's as a whole: half were built before 1963 (1976 for Indiana), and 47% date from before 1960. 66% of occupied homes are lived in by their owner (Indiana: 70%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Knox County, Indiana, 2019 to 2023
HomesKnox CountyIndiana
Housing units16,9652,953,344
Detached houses75%73%
In buildings of 5 or more8%13%
Mobile homes5%4%
Built before 196047%32%
Built since 20008%21%
Middle year built19631976
Owner-occupied66%70%

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