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Radon Levels in McLean County, Illinois

EPA puts McLean County in Zone 1, its highest radon zone, and high results are common there: 42.5% of the 4,548 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

    42.5%

    8.8 pts above IL

    McLean
    42.5%
    Illinois
    33.7%

    4,548 tests, 2017

  • Median result

    3.3pCi/L

    Below action level

    McLean
    3.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    4,548

    9th of 70 by tests

    McLean
    4,548
    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

    38 of 70

    Middle half

    McLean
    42.5%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for McLean County

Starts at McLean County's median, 3.3 pCi/L

3.3pCi/L

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

EPA’s reading of 3.3 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. McLean County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

McLean County, At a glance

McLean County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of McLean 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 McLean County, 2017

Share of reported tests at or above 4 pCi/L, by year, McLean County
Share of reported tests at or above 4 pCi/L, by year, McLean County
YearShare of reported tests at or above 4 pCi/L
201449.0%
201545.2%
201636.8%
201742.5%

2017: 42.5%. Across these years the share ran from 36.8% to 49.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 4,548 tests reported to CDC for McLean 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

McLean County, Compared

McLean County radon figures, compared

Calculated by Radon411

In McLean County, about 4 in 10 reported tests in 2017 (1,932 of 4,548) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 10.8 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so McLean County runs 8.8 points above its state.

Of 8 neighbours with a figure, all 8 reported a larger share at or above 4 pCi/L; the spread is 44.7% (Champaign County) to 61.7% (Livingston County). By share, McLean County is 38th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 49.0% and 2017 closed at 42.5% (down 6.5 points), with 2014 the high at 49.0%. Half the tests came in under 3.3 pCi/L and half over it; the single highest reached 54.2 pCi/L. Below the action level, 1,482 tests (32.6%) came in under 2 pCi/L, against 37.7% statewide, and 1,134 tests (24.9%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 42.5% share point the same way here. USGS geology rates 100% of the county's land high radon potential.

The busiest year on file was 2014, with 7,518 tests reported; the quietest, 2016, had 261.

Share of reported tests at or above 4 pCi/L by year, McLean County against Illinois2014 to 2017, years with 30 or more tests: McLean County 49.0% to 42.5%, the state's pooled share 33.7% in 2017.
McLean CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, McLean County against Illinois: data table
YearTestsMcLean County, at or above 4 pCi/LIllinois, pooled
20147,51849.0%37.8%
20154,22445.2%36.6%
201626136.8%17.4%
20174,54842.5%33.7%
McLean County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from McLean County
McLean County4,54842.5%3.3 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−8.8 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−10.8 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+26.7 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−34.1 points
Livingston County, ILborders it34561.7%5.3 pCi/L+19.2 points
Ford County, ILborders it4257.1%4.0 pCi/L+14.6 points
De Witt County, ILborders it12657.1%5.2 pCi/L+14.6 points
Piatt County, ILborders it27954.8%4.3 pCi/L+12.3 points
Woodford County, ILborders it76552.9%4.2 pCi/L+10.4 points
Tazewell County, ILborders it2,72446.4%3.6 pCi/L+3.9 points
Logan County, ILborders it7245.8%3.4 pCi/L+3.3 points
Champaign County, ILborders it3,15944.7%3.4 pCi/L+2.2 points
Where McLean County's reported results fell, 2017, beside Illinois and the United States
ResultMcLean County testsMcLean County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L1,48232.6%37.7%43.5%−5.1 points
2 to 4 pCi/L1,13424.9%28.6%24.8%−3.7 points
4 pCi/L and above1,93242.5%33.7%31.7%+8.8 points
McLean 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
Champaign County33 of 703,15944.7%3.4 pCi/L
Montgomery County34 of 7012343.9%3.3 pCi/L
Lee County35 of 7021943.8%3.3 pCi/L
Sangamon County36 of 703,37843.7%3.7 pCi/L
Whiteside County37 of 7069643.1%3.3 pCi/L
McLean County38 of 704,54842.5%3.3 pCi/L
Christian County39 of 7021342.3%3.5 pCi/L
DeKalb County40 of 701,70741.1%3.3 pCi/L
Peoria County41 of 703,81640.2%3.1 pCi/L
Will County42 of 7010,77640.0%3.1 pCi/L
Monroe County43 of 7071439.9%3.0 pCi/L
McLean County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20174,54842.5%3.3 pCi/L54.2 pCi/L33.7%+5.7 points
201626136.8%3.0 pCi/L13.9 pCi/L17.4%−8.4 points
20154,22445.2%3.5 pCi/L70.6 pCi/L36.6%−3.8 points
20147,51849.0%3.8 pCi/L39.7 pCi/L37.8%First on file

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

McLean County, Geology

The ground under McLean County

Predicted

USGS's geologic map puts all of McLean County's mapped land in one class: high radon potential. All 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 McLean County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High13100%

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

McLean County beside the ground around it

McLean County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 8 counties that border it, none has as large a share of high-potential ground; Champaign County comes nearest at 100%.

Share of land by USGS radon potential: McLean County, the 8 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
McLean CountyZone 1NoneNone100%
De Witt CountyZone 1NoneNone100%
Woodford CountyZone 1NoneNone100%
Livingston CountyZone 1NoneNone100%
Tazewell CountyZone 1NoneNone100%
Logan CountyZone 1NoneNone100%
Piatt CountyZone 1NoneNone100%
Ford CountyZone 1None0.8%99.2%
Champaign CountyZone 1NoneNone100%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

McLean County, Local resources

Radon testing and mitigation in McLean County

Listed radon businesses with an address in McLean County:

Listed radon professionals by town: Bloomington, Normal, Heyworth, Chenoa

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

McLean County, Questions

Questions about radon in McLean County

Are radon levels high in McLean County?

In 2017, 42.5% of the radon tests reported to CDC for McLean County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.3 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 37 reported a higher share; pooled, the state comes to 33.7%.

Which counties border McLean County?

McLean County borders 8 counties: De Witt County, Woodford County, Livingston County, Tazewell County, Logan County, Piatt County, Ford County and Champaign County.

Products

McLean County, Products

Testing a home in McLean County

In McLean County, 42.5% of 4,548 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in McLean 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

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

Explore

McLean County, Bordering counties

Counties bordering McLean County

Calculated by Radon411

McLean County, Cities and towns

Cities and towns in McLean County

McLean County's population has barely moved since 2020: 171,419 residents on July 1, 2025 against 171,210 then, by the Census Bureau's estimates. That works out to 145 people per square mile of land. Its largest town, Bloomington, has 78,804 residents, 46.0% of the total. Testing is reported here more often than across the state: CDC's 4,548 reported tests for 2017 come to 26.5 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.

From Bloomington to Cooksville, CDC publishes no figure by town: each reads McLean County's.

The 12 largest cities and towns in McLean County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Bloomington78,804+0.2%46.0%
Normal53,275+0.5%31.1%
Le Roy3,465−1.5%2.0%
Heyworth2,869+2.7%1.7%
El Pasoextends beyond McLean County2,723−0.9%Counted whole
Lexington2,079−0.6%1.2%
Hudson1,750−0.3%1.0%
Chenoa1,705−0.6%1.0%
Gridley1,428−1.7%0.8%
Downs1,173−1.8%0.7%
Danvers1,062−2.2%0.6%
Colfax973−2.0%0.6%
  • McLean
  • Saybrook
  • Carlock
  • Stanford
  • Towanda
  • Bellflower
  • Arrowsmith
  • Ellsworth
  • Anchor
  • Cooksville

22 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond McLean County is counted whole, so it has no share.

McLean County, Homes

Homes in McLean County

Of McLean County's 75,120 homes, 60% are detached houses, against 58% across Illinois; 24% are in buildings of five or more homes. Much of McLean County is recent building: 24% of its homes have gone up since 2000 and the middle year built is 1981, against 1970 for Illinois. 65% 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 McLean County, Illinois, 2019 to 2023
HomesMcLean CountyIllinois
Housing units75,1205,443,501
Detached houses60%58%
In buildings of 5 or more24%22%
Mobile homes4%2%
Built before 196023%38%
Built since 200024%16%
Middle year built19811970
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.