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Radon Levels in Coles County, Illinois

EPA puts Coles County in Zone 1, its highest radon zone, and high results are common there: 51.5% of the 198 radon tests reported to CDC (2017) 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    51.5%

    17.8 pts above IL

    Coles
    51.5%
    Illinois
    33.7%

    198 tests, 2017

  • Median result

    4.2pCi/L

    Action level reached

    Coles
    4.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    198

    43rd of 70 by tests

    Coles
    198
    Cook
    26,937

    Reported to CDC before any fix, 2017

  • 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 Illinois

    20 of 70

    Middle half

    Coles
    51.5%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Coles County

Starts at Coles County's median, 4.2 pCi/L

4.2pCi/L

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

EPA’s reading of 4.2 pCi/L

At or above 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 at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Coles County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Coles County, At a glance

Coles County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Coles 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 98% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Coles County, 2017

Share of reported tests at or above 4 pCi/L, by year, Coles County
Share of reported tests at or above 4 pCi/L, by year, Coles County
YearShare of reported tests at or above 4 pCi/L
201449.2%
201532.7%
201751.5%

2017: 51.5%. Across these years the share ran from 32.7% to 51.5%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 198 tests reported to CDC for Coles 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

Coles County, Compared

Coles County radon figures, compared

Calculated by Radon411

More than half: 51.5% of the 198 radon tests reported to CDC for Coles County in 2017 read at least 4 pCi/L. That places it 20th of 70 Illinois counties with 30 or more tests for the same period. That is 17.8 points above the 33.7% pooled from 93 Illinois counties.

The median result, 4.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 29.1 pCi/L. The rest split 19.7% under 2 pCi/L and 28.8% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 51.5% share point the same way here.

No bordering county with a figure for the same period reported a higher share; the closest is Douglas County at 50.0%, the lowest Moultrie County at 46.7%. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).

The busiest year on file was 2014, with 354 tests reported; the quietest, 2015, had 156.

Over 3 years of annual figures the share rose 2.3 points, from 49.2% in 2014 to 51.5% in 2017; its peak was 51.5% in 2017. Nationally, every county with a figure for the same period pools to 31.7%; Coles County sits 19.8 points above it.

Share of reported tests at or above 4 pCi/L by year, Coles County against Illinois2014 to 2017, years with 30 or more tests: Coles County 49.2% to 51.5%, the state's pooled share 33.7% in 2017.
Coles CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Coles County against Illinois: data table
YearTestsColes County, at or above 4 pCi/LIllinois, pooled
201435449.2%37.8%
201515632.7%36.6%
201719851.5%33.7%
Coles County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Coles County
Coles County19851.5%4.2 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−17.8 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−19.8 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+17.7 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−43.1 points
Shelby County, ILborders it2171.4%5.2 pCi/L+19.9 points
Edgar County, ILborders it2157.1%4.5 pCi/L+5.6 points
Douglas County, ILborders it8450.0%3.8 pCi/L−1.5 points
Moultrie County, ILborders it4546.7%3.3 pCi/L−4.8 points
Clark County, ILborders it933.3%3.1 pCi/L−18.2 points
Cumberland County, ILborders it1225.0%2.8 pCi/L−26.5 points
Where Coles County's reported results fell, 2017, beside Illinois and the United States
ResultColes County testsColes County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L3919.7%37.7%43.5%−18.0 points
2 to 4 pCi/L5728.8%28.6%24.8%+0.2 points
4 pCi/L and above10251.5%33.7%31.7%+17.8 points
Coles 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
Vermilion County15 of 703953.8%4.7 pCi/L
Putnam County16 of 704553.3%4.5 pCi/L
Woodford County17 of 7076552.9%4.2 pCi/L
Ogle County18 of 7063652.4%4.1 pCi/L
Menard County19 of 7016851.8%4.3 pCi/L
Coles County20 of 7019851.5%4.2 pCi/L
Douglas County21 of 708450.0%3.8 pCi/L
Warren County21 of 704250.0%3.6 pCi/L
Marshall County23 of 708148.1%3.8 pCi/L
Boone County24 of 7052546.9%3.4 pCi/L
Moultrie County25 of 704546.7%3.3 pCi/L
Coles County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201719851.5%4.2 pCi/L29.1 pCi/L33.7%+18.8 points
201515632.7%2.8 pCi/L14.6 pCi/L36.6%−16.5 points
201435449.2%3.9 pCi/L12.6 pCi/L37.8%First on file

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

Coles County, Geology

The ground under Coles County

Predicted

Most of the ground under Coles County is one class on USGS's geologic map: 98.1% of its land is high radon potential, with 1.9% moderate. 98.1% of it lies in the area the map calls Bloomington Ridged Plain, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Coles County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High1398.1%
Southern Central Lowland ProvinceIllinoian glacial deposits, sandstone, and gray shale.Moderate91.9%

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

Coles County beside the ground around it

Coles County has more high-potential ground than Illinois as a whole: 98.1% of its land against 64.5%. Of the 6 counties that border it, 2 have more high-potential ground, Douglas County the most at 100%.

Share of land by USGS radon potential: Coles County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Coles CountyZone 1None1.9%98.1%
Douglas CountyZone 1NoneNone100%
Cumberland CountyZone 2None94.7%5.3%
Moultrie CountyZone 1NoneNone100%
Edgar CountyZone 1None5.1%94.9%
Clark CountyZone 2None96.5%3.5%
Shelby CountyZone 2None54.9%45.1%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Coles County, Local resources

Radon testing and mitigation in Coles 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

Coles County, Questions

Questions about radon in Coles County

Are radon levels high in Coles County?

In 2017, 51.5% of the radon tests reported to CDC for Coles County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.2 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 19 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Coles County?

Coles County borders 6 counties: Douglas County, Cumberland County, Moultrie County, Edgar County, Clark County and Shelby County.

Products

Coles County, Products

Testing a home in Coles County

In Coles County, 51.5% of 198 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Coles 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

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

Explore

Coles County, Bordering counties

Counties bordering Coles County

Calculated by Radon411

Coles County, Cities and towns

Cities and towns in Coles County

About 46,607 people live in Coles County by the Census Bureau's estimate for July 1, 2025, 480 fewer than in 2020 (−1.0%). That works out to 92 people per square mile of land. Its largest town, Charleston, has 17,466 residents, 37.5% of the total. Together its 6 incorporated places hold 77.4% of those residents; the other 22.6% live outside any of them. Reported testing is thin here: 198 tests over 2017, or 4.2 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.

From Charleston to Lerna, CDC publishes no figure by town: each reads Coles County's.

The cities and towns in Coles County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Charleston17,466−0.6%37.5%
Mattoon16,667−1.1%35.8%
Oakland721−1.6%1.5%
Ashmore627−1.6%1.3%
Humboldt354−1.7%0.8%
Lerna216−2.3%0.5%

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).

Coles County, Homes

Homes in Coles County

Of Coles County's 22,717 homes, 68% are detached houses, against 58% across Illinois; 17% are in buildings of five or more homes. Half of its homes were built before 1970, close to Illinois' 1970: 40% date from before 1960 and 12% from 2000 or later. 60% 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 Coles County, Illinois, 2019 to 2023
HomesColes CountyIllinois
Housing units22,7175,443,501
Detached houses68%58%
In buildings of 5 or more17%22%
Mobile homes4%2%
Built before 196040%38%
Built since 200012%16%
Middle year built19701970
Owner-occupied60%67%

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