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Radon Levels in Jefferson County, Illinois

EPA puts Jefferson County in Zone 2, its middle radon zone, and 19.6% of its 138 reported radon tests (2017) 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    19.6%

    14.1 pts below IL

    Jefferson
    19.6%
    Illinois
    33.7%

    138 tests, 2017

  • Median result

    1.9pCi/L

    Below action level

    Jefferson
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    138

    47th of 70 by tests

    Jefferson
    138
    Cook
    26,937

    Reported to CDC before any fix, 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 Illinois

    66 of 70

    Lowest quarter

    Jefferson
    19.6%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Jefferson County

Starts at Jefferson 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. Jefferson County's median reported result, 2017.

Interpret this reading

The data

Jefferson County, At a glance

Jefferson County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Jefferson 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 Jefferson County, 2017

Share of reported tests at or above 4 pCi/L, by year, Jefferson County
Share of reported tests at or above 4 pCi/L, by year, Jefferson County
YearShare of reported tests at or above 4 pCi/L
201427.3%
201530.3%
201719.6%

2017: 19.6%. Across these years the share ran from 19.6% to 30.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 138 tests reported to CDC for Jefferson County over 2017, 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: 2017. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Jefferson County, Compared

Jefferson County radon figures, compared

Calculated by Radon411

Jefferson County's 138 reported tests in 2017 had a middle value of 1.9 pCi/L and a maximum of 9.3 pCi/L, and 19.6% reached 4 pCi/L. Illinois as a whole (93 Illinois counties, pooled) comes to 33.7%: 14.1 points higher than here.

Among its state's counties it ranks 66th of 70 Illinois counties with 30 or more tests for the same period. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).

Below the action level, 78 tests (56.5%) came in under 2 pCi/L, against 37.7% statewide, and 33 tests (23.9%) fell between 2 and 4, against 28.6% statewide. The busiest year on file was 2017, with 138 tests reported; the quietest, 2015, had 99.

EPA's 1993 zone map puts Jefferson 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 10.0% in Franklin County to 20.0% in Marion County, with Washington County and Franklin County below Jefferson County. Over 3 years of annual figures the share fell 7.7 points, from 27.3% in 2014 to 19.6% in 2017; its peak was 30.3% in 2015.

Share of reported tests at or above 4 pCi/L by year, Jefferson County against Illinois2014 to 2017, years with 30 or more tests: Jefferson County 27.3% to 19.6%, the state's pooled share 33.7% in 2017.
Jefferson CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Jefferson County against Illinois: data table
YearTestsJefferson County, at or above 4 pCi/LIllinois, pooled
201413227.3%37.8%
20159930.3%36.6%
201713819.6%33.7%
Jefferson County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Jefferson County
Jefferson County13819.6%1.9 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled+14.1 points
United States, pooled937 counties, pooled528,06231.7%Not pooled+12.1 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+49.6 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−11.2 points
Perry County, ILborders it1540.0%1.5 pCi/L+20.4 points
Marion County, ILborders it4520.0%1.9 pCi/L+0.4 points
Washington County, ILborders it5111.8%2.0 pCi/L−7.8 points
Franklin County, ILborders it3010.0%1.9 pCi/L−9.6 points
Wayne County, ILborders it60.0%1.6 pCi/L−19.6 points
Where Jefferson County's reported results fell, 2017, beside Illinois and the United States
ResultJefferson County testsJefferson County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L7856.5%37.7%43.5%+18.8 points
2 to 4 pCi/L3323.9%28.6%24.8%−4.7 points
4 pCi/L and above2719.6%33.7%31.7%−14.1 points
Jefferson County ranked among the 70 Illinois counties with 30 or more tests, by share at or above 4 pCi/L, 2017
CountyRankTestsAt or above 4 pCi/LMedian
Fayette County60 of 705726.3%2.5 pCi/L
Macoupin County61 of 7025825.6%2.2 pCi/L
Jackson County62 of 709625.0%2.5 pCi/L
Iroquois County62 of 703625.0%1.9 pCi/L
Mason County64 of 704221.4%2.8 pCi/L
Marion County65 of 704520.0%1.9 pCi/L
Jefferson County66 of 7013819.6%1.9 pCi/L
Cook County67 of 7026,93719.4%1.9 pCi/L
Washington County68 of 705111.8%2.0 pCi/L
Franklin County69 of 703010.0%1.9 pCi/L
Williamson County70 of 702498.4%0.9 pCi/L
Jefferson County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201713819.6%1.9 pCi/L9.3 pCi/L33.7%−10.7 points
20159930.3%3.0 pCi/L18.7 pCi/L36.6%+3.0 points
201413227.3%2.2 pCi/L9.8 pCi/L37.8%First on file

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

Jefferson County, Geology

The ground under Jefferson County

Predicted

USGS's geologic map puts all of Jefferson County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Southern Central Lowland Province, to which USGS gives a radon index of 9, in the moderate band (9 to 11).

USGS's geologic areas under Jefferson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Southern Central Lowland ProvinceIllinoian glacial deposits, sandstone, and gray shale.Moderate9100%

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

Jefferson County beside the ground around it

Across Illinois 64.5% of the land is rated high; none of Jefferson County's is. Of the 6 counties that border it, none has as large a share of moderate-potential ground; Franklin County comes nearest at 100%.

Share of land by USGS radon potential: Jefferson County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Jefferson CountyZone 2None100%None
Marion CountyZone 2None100%None
Franklin CountyZone 2None100%None
Wayne CountyZone 2None100%None
Washington CountyZone 2None100%None
Perry CountyZone 2None100%None
Hamilton CountyZone 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

Jefferson County, Local resources

Radon testing and mitigation in Jefferson County

Listed radon businesses with an address in Jefferson County:

Listed radon professionals by town: Waltonville

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

Jefferson County, Questions

Questions about radon in Jefferson County

Are radon levels high in Jefferson County?

In 2017, 19.6% of the radon tests reported to CDC for Jefferson County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 65 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Jefferson County?

Jefferson County borders 6 counties: Marion County, Franklin County, Wayne County, Washington County, Perry County and Hamilton County.

Products

Jefferson County, Products

Testing a home in Jefferson County

In Jefferson County, 19.6% of 138 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Jefferson County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Jefferson County homes, compared

Explore

Jefferson County, Bordering counties

Counties bordering Jefferson County

Calculated by Radon411

Jefferson County, Cities and towns

Cities and towns in Jefferson County

About 36,147 people live in Jefferson County by the Census Bureau's estimate for July 1, 2025, 851 fewer than in 2020 (−2.3%). That works out to 63 people per square mile of land. Its largest town, Mount Vernon, has 14,187 residents, 39.2% of the total. Reported testing is thin here: 138 tests over 2017, or 3.8 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.

From Mount Vernon to Nason, CDC publishes no figure by town: each reads Jefferson County's.

The cities and towns in Jefferson County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Mount Vernon14,187−2.6%39.2%
Centraliaextends beyond Jefferson County11,863−2.1%Counted whole
Ina1,612−2.2%4.5%
Woodlawn611−1.6%1.7%
Bluford607−2.6%1.7%
Dix456−2.1%1.3%
Waltonville406−2.2%1.1%
Bonnie365−1.6%1.0%
Belle Rive307−1.9%0.8%
Nason198−1.5%0.5%

10 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 Jefferson County is counted whole, so it has no share.

Jefferson County, Homes

Homes in Jefferson County

Of Jefferson County's 16,650 homes, 70% are detached houses, against 58% across Illinois; 17% are mobile homes. Half of its homes were built before 1977, close to Illinois' 1970: 29% date from before 1960 and 17% from 2000 or later. 72% of occupied homes are lived in by their owner (Illinois: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Jefferson County, Illinois, 2019 to 2023
HomesJefferson CountyIllinois
Housing units16,6505,443,501
Detached houses70%58%
In buildings of 5 or more8%22%
Mobile homes17%2%
Built before 196029%38%
Built since 200017%16%
Middle year built19771970
Owner-occupied72%67%

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