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Radon Levels in Cook County, Illinois

EPA puts Cook County in Zone 2, its middle radon zone, and 19.4% of its 26,937 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

    19.4%

    14.3 pts below IL

    Cook
    19.4%
    Illinois
    33.7%

    26,937 tests, 2017

  • Median result

    1.9pCi/L

    Below action level

    Cook
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    26,937

    Most tested in Illinois

    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

    67 of 70

    Lowest quarter

    Cook
    19.4%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Cook County

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

Interpret this reading

The data

Cook County, At a glance

Cook County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Cook 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 97% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Cook County, 2017

Share of reported tests at or above 4 pCi/L, by year, Cook County
Share of reported tests at or above 4 pCi/L, by year, Cook County
YearShare of reported tests at or above 4 pCi/L
201420.5%
201522.3%
20169.3%
201719.4%

2017: 19.4%. Across these years the share ran from 9.3% to 22.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 26,937 tests reported to CDC for Cook 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

Cook County, Compared

Cook County radon figures, compared

Calculated by Radon411

Cook County's 26,937 reported tests in 2017 had a middle value of 1.9 pCi/L and a maximum of 101.4 pCi/L, and 19.4% reached 4 pCi/L. Illinois as a whole (93 Illinois counties, pooled) comes to 33.7%: 14.3 points higher than here.

Among its state's counties it ranks 67th 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, 14,001 tests (52.0%) came in under 2 pCi/L, against 37.7% statewide, and 7,698 tests (28.6%) fell between 2 and 4, against 28.6% statewide. The busiest year on file was 2014, with 36,777 tests reported; the quietest, 2016, had 2,313.

EPA's 1993 zone map puts Cook County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 97% of the county's land moderate radon potential.

Next door, the shares run from 27.4% in Lake County to 40.0% in Will County. Over 4 years of annual figures the share held within 2 points, from 20.5% in 2014 to 19.4% in 2017; its peak was 22.3% in 2015.

Share of reported tests at or above 4 pCi/L by year, Cook County against Illinois2014 to 2017, years with 30 or more tests: Cook County 20.5% to 19.4%, the state's pooled share 33.7% in 2017.
Cook CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Cook County against Illinois: data table
YearTestsCook County, at or above 4 pCi/LIllinois, pooled
201436,77720.5%37.8%
201519,16122.3%36.6%
20162,3139.3%17.4%
201726,93719.4%33.7%
Cook County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Cook County
Cook County26,93719.4%1.9 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled+14.3 points
United States, pooled937 counties, pooled528,06231.7%Not pooled+12.3 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+49.8 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−11.0 points
Will County, ILborders it10,77640.0%3.1 pCi/L+20.6 points
Kane County, ILborders it8,68236.6%2.8 pCi/L+17.2 points
McHenry County, ILborders it6,47435.1%2.9 pCi/L+15.7 points
DuPage County, ILborders it19,40133.7%2.7 pCi/L+14.3 points
Lake County, ILborders it13,05027.4%2.4 pCi/L+8.0 points
Where Cook County's reported results fell, 2017, beside Illinois and the United States
ResultCook County testsCook County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L14,00152.0%37.7%43.5%+14.3 points
2 to 4 pCi/L7,69828.6%28.6%24.8%Level
4 pCi/L and above5,23819.4%33.7%31.7%−14.3 points
Cook 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
Cook County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201726,93719.4%1.9 pCi/L101.4 pCi/L33.7%+10.1 points
20162,3139.3%1.1 pCi/L20.5 pCi/L17.4%−13.0 points
201519,16122.3%2.1 pCi/L79.6 pCi/L36.6%+1.8 points
201436,77720.5%2.0 pCi/L129.2 pCi/L37.8%First on file

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

Cook County, Geology

The ground under Cook County

Predicted

Most of the ground under Cook County is one class on USGS's geologic map: 96.8% of its land is moderate radon potential, with 3.2% high. 96.8% of it lies in the area the map calls Wheaton Morainal Country, to which USGS gives a radon index of 11, in the moderate band (9 to 11).

USGS's geologic areas under Cook County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Wheaton Morainal CountryGlacial lake deposits and clay-rich glacial till.Moderate1196.8%
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High133.2%

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

Cook County beside the ground around it

Illinois as a whole has more high-potential ground than Cook County: 64.5% of its land, against 3.2% here. Of the 6 counties that border it, 5 have more high-potential ground, McHenry County the most at 100%.

Share of land by USGS radon potential: Cook County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Cook CountyZone 2None96.8%3.2%
DuPage CountyZone 2None80.1%19.9%
Will CountyZone 2None40.2%59.8%
Lake County, INZone 2None99.3%None
Kane CountyZone 1NoneNone100%
Lake CountyZone 2None85.8%14.1%
McHenry CountyZone 2NoneNone100%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Cook County, Local resources

Radon testing and mitigation in Cook County

Listed radon businesses with an address in Cook County:

Listed radon professionals by town: Chicago, Elgin, Schaumburg, Arlington Heights, Palatine, Orland Park, Oak Lawn, Mount Prospect, Tinley Park, Berwyn, Oak Park, Hoffman Estates, Elmhurst, Buffalo Grove, Park Ridge, Streamwood, Hanover Park, Northbrook, Woodridge, Elk Grove Village, Niles, Oak Forest, Homer Glen, Morton Grove, Maywood, South Holland, Deerfield, Matteson, Bensenville, Lemont, Westchester, La Grange, Midlothian, La Grange Park, Lincolnwood, Palos Heights, Summit, Barrington, Countryside

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

Cook County, Questions

Questions about radon in Cook County

Are radon levels high in Cook County?

In 2017, 19.4% of the radon tests reported to CDC for Cook 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, 66 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Cook County?

Cook County borders 6 counties: DuPage County, IL, Will County, IL, Lake County, IN, Kane County, IL, Lake County, IL and McHenry County, IL.

Products

Cook County, Products

Testing a home in Cook County

In Cook County, 19.4% of 26,937 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 Cook County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Cook County homes, compared

Explore

Cook County, Bordering counties

Counties bordering Cook County

Calculated by Radon411

Cook County, Cities and towns

Cities and towns in Cook County

About 5,194,625 people live in Cook County by the Census Bureau's estimate for July 1, 2025, 69,026 fewer than in 2020 (−1.3%). Packed into its land, that is 5,497 people per square mile. Chicago, the largest place on its list (2,731,585 residents in all), extends beyond Cook County, so no share of the total is worked out for it. Reported testing is thin here: 26,937 tests over 2017, or 5.2 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.

From Chicago to McCook, CDC publishes no figure by town: each reads Cook County's.

The 12 largest cities and towns in Cook County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Chicagoextends beyond Cook County2,731,585−0.4%Counted whole
Elginextends beyond Cook County115,476+0.8%Counted whole
Cicero81,858−3.6%1.6%
Schaumburgextends beyond Cook County77,249−1.5%Counted whole
Evanston76,380−1.9%1.5%
Arlington Heights76,216−1.5%1.5%
Skokie66,544−1.7%1.3%
Palatine65,842−2.7%1.3%
Des Plaines58,772−2.8%1.1%
Orland Parkextends beyond Cook County57,954−1.0%Counted whole
Oak Lawn56,450−2.9%1.1%
Mount Prospect55,395−2.3%1.1%
  • Tinley Park (part)
  • Berwyn
  • Oak Park
  • Hoffman Estates (part)
  • Elmhurst (part)
  • Buffalo Grove (part)
  • Bartlett (part)
  • Park Ridge
  • Wheeling (part)
  • Streamwood
  • Hanover Park (part)
  • Calumet City
  • Northbrook
  • Woodridge (part)
  • Elk Grove Village (part)
  • Niles
  • Burbank
  • Lansing
  • Wilmette
  • Oak Forest
  • Chicago Heights
  • Homer Glen (part)
  • Morton Grove
  • Melrose Park
The other 99 places in Cook County
  • Rolling Meadows
  • Elmwood Park
  • Maywood
  • Roselle (part)
  • Blue Island
  • Frankfort (part)
  • Park Forest (part)
  • South Holland
  • Dolton
  • Harvey
  • Deerfield (part)
  • Evergreen Park
  • Brookfield
  • Homewood
  • Matteson
  • Bensenville (part)
  • Lemont (part)
  • Alsip
  • Bellwood
  • Franklin Park
  • Palos Hills
  • Hinsdale (part)
  • Bridgeview
  • Westchester
  • Country Club Hills
  • La Grange
  • Prospect Heights
  • Norridge
  • Hickory Hills
  • Chicago Ridge
  • Midlothian
  • Forest Park
  • Western Springs
  • La Grange Park
  • Lincolnwood
  • Hazel Crest
  • Winnetka
  • Richton Park
  • Northlake
  • Justice
  • Palos Heights
  • River Forest
  • Schiller Park
  • Markham
  • Burr Ridge (part)
  • Summit
  • Worth
  • Barrington (part)
  • Crestwood
  • Lyons
  • River Grove
  • Riverdale
  • Sauk Village
  • Flossmoor
  • Steger (part)
  • Lynwood
  • Riverside
  • Harwood Heights
  • Glencoe
  • Glenwood
  • Crete (part)
  • Hillside
  • Broadview
  • Inverness
  • North Riverside
  • University Park (part)
  • Stickney
  • Calumet Park
  • Orland Hills
  • Countryside
  • Willow Springs
  • Northfield
  • Posen
  • Berkeley
  • South Barrington
  • Palos Park
  • Olympia Fields
  • Robbins
  • Stone Park
  • Hometown
  • Barrington Hills (part)
  • Indian Head Park
  • Burnham
  • South Chicago Heights
  • Rosemont
  • Deer Park (part)
  • East Dundee (part)
  • Dixmoor
  • Kenilworth
  • Thornton
  • Merrionette Park
  • Ford Heights
  • Phoenix
  • Hodgkins
  • East Hazel Crest
  • Forest View
  • Bedford Park
  • Golf
  • McCook

136 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 Cook County is counted whole, so it has no share.

Cook County, Homes

Homes in Cook County

Cook County has 2,270,349 homes, and many share a building: 34% are in buildings of five or more, 40% are detached houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1961 (1970 for Illinois), and 49% date from before 1960. 58% 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 Cook County, Illinois, 2019 to 2023
HomesCook CountyIllinois
Housing units2,270,3495,443,501
Detached houses40%58%
In buildings of 5 or more34%22%
Mobile homes1%2%
Built before 196049%38%
Built since 200012%16%
Middle year built19611970
Owner-occupied58%67%

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