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Radon Levels in Union County, Illinois

EPA puts Union County in Zone 2, its middle radon zone, and only 21 radon tests from it are on file with CDC (2017). 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

    23.7%

    20.6 pts below IL

    Union
    23.7%
    Illinois
    44.3%

    118 tests, 2006 to 2015

  • Median result

    1.9pCi/L

    Below action level

    Union
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2006 to 2015

  • Tests reported

    118

    65th of 92 by tests

    Union
    118
    Cook
    12,801

    Reported to CDC before any fix, 2006 to 2015

  • 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 Illinois

    76 of 92

    Lowest quarter

    Union
    23.7%
    Stark
    83.3%

    By share, of 92 with 30+ tests

Read a result for Union County

Starts at Union County'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. Union County's median reported result, 2006 to 2015.

Interpret this reading

The data

Union County, At a glance

Union County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Union 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 Union County, 2017

Share of reported tests at or above 4 pCi/L, by year, Union County
Share of reported tests at or above 4 pCi/L, by year, Union County
YearShare of reported tests at or above 4 pCi/L
20140.0%
201533.3%
20170.0%

2017: 0.0%. Across these years the share ran from 0.0% to 33.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 21 tests were reported to CDC for Union County over 2017, 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: 2017. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Union County, Compared

Union County radon figures, compared

Calculated by Radon411

Union County's 118 reported tests over the 2006 to 2015 laboratory totals had a middle value of 1.9 pCi/L and a maximum of 20.9 pCi/L, and 23.7% reached 4 pCi/L. Illinois as a whole (102 Illinois counties, pooled) comes to 44.3%: 20.6 points higher than here.

The newest figure, in 2017, counts only 21 tests (0.0% at or above 4 pCi/L), too few to compare, so this reading uses the 118-test figure.

Among its state's counties it ranks 76th of 92 Illinois counties with 30 or more tests for the same period. Statewide for the same period, Stark County reported the highest share (83.3%) and Williamson County the lowest (14.1%).

Below the action level, 59 tests (50.0%) came in under 2 pCi/L, against 30.8% statewide, and 31 tests (26.3%) fell between 2 and 4, against 24.9% statewide. The busiest year on file was 2017, with 21 tests reported; the quietest, 2015, had 9.

EPA's 1993 zone map puts Union 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 14.1% in Williamson County to 37.7% in Cape Girardeau County, MO, with Johnson County and Williamson County below Union County.

Union County against Illinois, the United States and nearby counties, 2006 to 2015, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Union County
Union County11823.7%1.9 pCi/LThis county
Illinois, pooled102 counties, pooled99,33744.3%Not pooled+20.6 points
United States, pooled2,669 counties, pooled1,805,52836.3%Not pooled+12.6 points
Stark Countyhighest in the state6083.3%9.1 pCi/L+59.6 points
Massac Countylowest in the state3414.7%2.0 pCi/L−9.0 points
Cape Girardeau County, MOborders it21237.7%2.9 pCi/L+14.0 points
Alexander County, ILborders it1533.3%1.3 pCi/L+9.6 points
Jackson County, ILborders it49929.5%2.4 pCi/L+5.8 points
Perry County, MOborders it6829.4%2.7 pCi/L+5.7 points
Johnson County, ILborders it4914.3%1.8 pCi/L−9.4 points
Williamson County, ILborders it61114.1%1.3 pCi/L−9.6 points
Pulaski County, ILborders it1811.1%1.0 pCi/L−12.6 points
Where Union County's reported results fell, 2006 to 2015, laboratory, beside Illinois and the United States
ResultUnion County testsUnion County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L5950.0%30.8%39.4%+19.2 points
2 to 4 pCi/L3126.3%24.9%24.3%+1.4 points
4 pCi/L and above2823.7%44.3%36.3%−20.6 points
Union County ranked among the 92 Illinois counties with 30 or more tests, by share at or above 4 pCi/L, 2006 to 2015, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Wabash County71 of 923426.5%2.5 pCi/L
Perry County72 of 9218125.4%2.3 pCi/L
White County73 of 924025.0%2.5 pCi/L
Clark County74 of 926924.6%1.8 pCi/L
Washington County75 of 9212623.8%2.5 pCi/L
Union County76 of 9211823.7%1.9 pCi/L
Hamilton County77 of 923122.6%2.0 pCi/L
Jefferson County78 of 9231522.2%1.9 pCi/L
Cumberland County79 of 924721.3%1.7 pCi/L
Cook County80 of 9212,80121.1%1.8 pCi/L
Saline County81 of 928320.5%1.8 pCi/L
Union County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
2017210.0%2.3 pCi/L3.8 pCi/L33.7%−33.3 points
2015933.3%1.1 pCi/L5.6 pCi/L36.6%+33.3 points
2014180.0%1.6 pCi/L3.3 pCi/L37.8%First on file

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

Union County, Geology

The ground under Union County

Predicted

USGS's geologic map puts all of Union County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Shawnee Hills Section, to which USGS gives a radon index of 10, in the moderate band (9 to 11).

USGS's geologic areas under Union County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Shawnee Hills SectionUnglaciated Ordovician to Pennsylvanian limestone, sandstone, and shale.Moderate1099.8%

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

Union County beside the ground around it

Across Illinois 64.5% of the land is rated high; none of Union County's is. Of the 7 counties that border it, none has as large a share of moderate-potential ground; Jackson County comes nearest at 100%.

Share of land by USGS radon potential: Union County, the 7 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Union CountyZone 2None100%None
Pulaski CountyZone 378.9%21.1%None
Johnson CountyZone 22.7%97.3%None
Alexander CountyZone 345.4%54.6%None
Cape Girardeau County, MOZone 217.1%82.9%None
Jackson CountyZone 2None100%None
Williamson CountyZone 2None100%None
Perry County, MOZone 2None100%None
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Union County, Local resources

Radon testing and mitigation in Union County

What Illinois's program says
Phone
(800) 325-1245
Licensing of radon professionals
The Agency also licenses and regulates the individuals who provide radon measurement and mitigation to the public.
Disclosure when a home is sold or rented
Illinois Radon Awareness Act - This is the legislation that requires the seller to provide to the buyer of any interest in residential real property the IEMA-OHS pamphlet entitled "Radon Testing Guidelines for Real Estate Transactions" and the Illinois Disclosure of Information on Radon Hazards.

What it means

Union County, Questions

Questions about radon in Union County

Are radon levels high in Union County?

In 2017, 0.0% of the radon tests reported to CDC for Union County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.3 pCi/L. Of 92 Illinois counties with 30 or more tests for the same period, 75 reported a higher share; pooled, the state comes to 44.3%.

Which counties border Union County?

Union County borders 7 counties: Pulaski County, IL, Johnson County, IL, Alexander County, IL, Cape Girardeau County, MO, Jackson County, IL, Williamson County, IL and Perry County, MO.

Products

Union County, Products

Testing a home in Union County

In Union County, 23.7% of 118 tests reported to CDC over the 2006 to 2015 laboratory totals reached 4 pCi/L, against 44.3% pooled across Illinois. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Union County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Union County homes, compared

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Union County, Bordering counties

Counties bordering Union County

Calculated by Radon411

Union County, Cities and towns

Cities and towns in Union County

About 16,656 people live in Union County by the Census Bureau's estimate for July 1, 2025, 643 fewer than in 2020 (−3.7%). That works out to 40 people per square mile of land. Its largest town, Anna, has 4,096 residents, 24.6% of the total. Together its 6 incorporated places hold 46.5% of those residents; the other 53.5% live outside any of them. CDC's 118 reported tests for 2006 to 2015 work out to 7.1 per 1,000 residents (2025 estimate), close to Illinois' 7.8.

From Anna to Mill Creek, CDC publishes no figure by town: each reads Union County's.

The cities and towns in Union County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Anna4,096−4.3%24.6%
Jonesboro1,635−4.0%9.8%
Cobden1,024−4.4%6.1%
Dongola638−3.9%3.8%
Alto Pass300−3.8%1.8%
Mill Creek52−5.5%0.3%

6 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).

Union County, Homes

Homes in Union County

Union County is a place of houses on their own lots: 76% of its 7,861 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1975, close to Illinois' 1970: 34% date from before 1960 and 19% from 2000 or later. Owners live in 77% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Union County, Illinois, 2019 to 2023
HomesUnion CountyIllinois
Housing units7,8615,443,501
Detached houses76%58%
In buildings of 5 or more5%22%
Mobile homes14%2%
Built before 196034%38%
Built since 200019%16%
Middle year built19751970
Owner-occupied77%67%

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