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Radon Levels in Madison County, Illinois

EPA puts Madison County in Zone 2, its middle radon zone, and 29.5% of its 5,214 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

    29.5%

    4.2 pts below IL

    Madison
    29.5%
    Illinois
    33.7%

    5,214 tests, 2017

  • Median result

    2.6pCi/L

    Below action level

    Madison
    2.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    5,214

    7th of 70 by tests

    Madison
    5,214
    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

    58 of 70

    Lowest quarter

    Madison
    29.5%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Madison County

Starts at Madison County's median, 2.6 pCi/L

2.6pCi/L

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

EPA’s reading of 2.6 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. Madison County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Madison County, At a glance

Madison County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Madison 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 92% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Madison County, 2017

Share of reported tests at or above 4 pCi/L, by year, Madison County
Share of reported tests at or above 4 pCi/L, by year, Madison County
YearShare of reported tests at or above 4 pCi/L
201432.6%
201528.6%
201666.7%
201729.5%

2017: 29.5%. Across these years the share ran from 28.6% to 66.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 5,214 tests reported to CDC for Madison 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

Madison County, Compared

Madison County radon figures, compared

Calculated by Radon411

Madison County's 5,214 reported tests in 2017 had a middle value of 2.6 pCi/L and a maximum of 56.1 pCi/L, and 29.5% reached 4 pCi/L. Illinois as a whole (93 Illinois counties, pooled) comes to 33.7%: 4.2 points higher than here.

Among its state's counties it ranks 58th 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, 1,884 tests (36.1%) came in under 2 pCi/L, against 37.7% statewide, and 1,791 tests (34.3%) fell between 2 and 4, against 28.6% statewide. The busiest year on file was 2014, with 5,433 tests reported; the quietest, 2016, had 18.

EPA's 1993 zone map puts Madison County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 92% of the county's land moderate radon potential.

Next door, the shares run from 25.6% in St. Louis city, MO to 46.5% in Jersey County, with Macoupin County and St. Louis city, MO below Madison County. Over 3 years of annual figures the share fell 3.1 points, from 32.6% in 2014 to 29.5% in 2017; its peak was 32.6% in 2014.

Share of reported tests at or above 4 pCi/L by year, Madison County against Illinois2014 to 2017, years with 30 or more tests: Madison County 32.6% to 29.5%, the state's pooled share 33.7% in 2017.
Madison CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Madison County against Illinois: data table
YearTestsMadison County, at or above 4 pCi/LIllinois, pooled
20145,43332.6%37.8%
20154,03228.6%36.6%
20175,21429.5%33.7%
Madison County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Madison County
Madison County5,21429.5%2.6 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled+4.2 points
United States, pooled937 counties, pooled528,06231.7%Not pooled+2.2 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+39.7 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−21.1 points
Jersey County, ILborders it12946.5%3.6 pCi/L+17.0 points
Montgomery County, ILborders it12343.9%3.3 pCi/L+14.4 points
Clinton County, ILborders it58237.6%3.0 pCi/L+8.1 points
St. Charles County, MOborders it39835.9%2.8 pCi/L+6.4 points
St. Clair County, ILborders it5,19333.7%2.6 pCi/L+4.2 points
Bond County, ILborders it7532.0%2.6 pCi/L+2.5 points
St. Louis County, MOborders it45930.1%2.6 pCi/L+0.6 points
Macoupin County, ILborders it25825.6%2.2 pCi/L−3.9 points
St. Louis city, MOborders it8225.6%2.1 pCi/L−3.9 points
Where Madison County's reported results fell, 2017, beside Illinois and the United States
ResultMadison County testsMadison County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L1,88436.1%37.7%43.5%−1.6 points
2 to 4 pCi/L1,79134.3%28.6%24.8%+5.7 points
4 pCi/L and above1,53929.5%33.7%31.7%−4.2 points
Madison 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
DuPage County53 of 7019,40133.7%2.7 pCi/L
Hancock County54 of 706333.3%2.8 pCi/L
Grundy County55 of 7039032.3%2.4 pCi/L
Bond County56 of 707532.0%2.6 pCi/L
Kankakee County57 of 7052231.6%2.7 pCi/L
Madison County58 of 705,21429.5%2.6 pCi/L
Lake County59 of 7013,05027.4%2.4 pCi/L
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
Madison County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20175,21429.5%2.6 pCi/L56.1 pCi/L33.7%−37.2 points
20161866.7%4.3 pCi/L6.0 pCi/L17.4%+38.1 points
20154,03228.6%2.5 pCi/L31.2 pCi/L36.6%−4.0 points
20145,43332.6%2.8 pCi/L304.0 pCi/L37.8%First on file

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

Madison County, Geology

The ground under Madison County

Predicted

Most of the ground under Madison County is one class on USGS's geologic map: 91.7% of its land is moderate radon potential, with 8.3% high. The map puts 91.6% of Madison County in the area it calls Southern Central Lowland Province and 8.3% in Galesburg Plain. USGS gives the first a radon index of 9, in the moderate band (9 to 11), and the second 13, in the high band (12 to 17).

USGS's geologic areas under Madison County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Southern Central Lowland ProvinceIllinoian glacial deposits, sandstone, and gray shale.Moderate991.6%
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High138.3%

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

Madison County beside the ground around it

Illinois as a whole has more high-potential ground than Madison County: 64.5% of its land, against 8.3% here. Of the 9 counties that border it, 3 have more high-potential ground, Jersey County the most at 99.6%.

Share of land by USGS radon potential: Madison County, the 9 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Madison CountyZone 2None91.7%8.3%
Macoupin CountyZone 2None42.4%57.6%
Bond CountyZone 2None100%None
St. Louis city, MOZone 2None100%None
St. Clair CountyZone 2None100%None
Clinton CountyZone 2None100%None
Jersey CountyZone 1None0.4%99.6%
St. Louis County, MOZone 2None100%None
Montgomery CountyZone 2None88.8%11.2%
St. Charles 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

Madison County, Local resources

Radon testing and mitigation in Madison County

Listed radon businesses with an address in Madison County:

Listed radon professionals by town: Edwardsville, Alton, Collinsville, Godfrey, Troy, Highland, Maryville, East Alton

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

Madison County, Questions

Questions about radon in Madison County

Are radon levels high in Madison County?

In 2017, 29.5% of the radon tests reported to CDC for Madison County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.6 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 57 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Madison County?

Madison County borders 9 counties: Macoupin County, IL, Bond County, IL, St. Louis city, MO, St. Clair County, IL, Clinton County, IL, Jersey County, IL, St. Louis County, MO, Montgomery County, IL and St. Charles County, MO.

Products

Madison County, Products

Testing a home in Madison County

In Madison County, 29.5% of 5,214 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 Madison County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Madison County homes, compared

Explore

Madison County, Bordering counties

Counties bordering Madison County

Calculated by Radon411

Madison County, Cities and towns

Cities and towns in Madison County

About 263,110 people live in Madison County by the Census Bureau's estimate for July 1, 2025, 2,636 fewer than in 2020 (−1.0%). That works out to 368 people per square mile of land. No town dominates: Granite City, the largest, has 26,807 residents, 10.2% of the total. Testing is reported here more often than across the state: CDC's 5,214 reported tests for 2017 come to 19.8 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.

From Granite City to Williamson, CDC publishes no figure by town: each reads Madison County's.

The 12 largest cities and towns in Madison County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Granite City26,807−2.6%10.2%
Edwardsville26,463−1.3%10.1%
Alton25,013−2.4%9.5%
Collinsvilleextends beyond Madison County23,717−2.7%Counted whole
Godfrey17,620−1.0%6.7%
Glen Carbon13,898+0.3%5.3%
Troy11,893+4.0%4.5%
Wood River10,224−2.0%3.9%
Highland10,042−0.3%3.8%
Bethalto9,202−1.1%3.5%
Maryville8,413+1.9%3.2%
Pontoon Beach5,887+0.4%2.2%
  • East Alton
  • Madison (part)
  • Fairmont City (part)
  • South Roxana
  • Venice
  • Roxana
  • St. Jacob
  • Hartford
  • Worden
  • Marine
  • Hamel
  • Livingston
  • Alhambra
  • Pierron (part)
  • New Douglas
  • Grantfork
  • Williamson

29 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 Madison County is counted whole, so it has no share.

Madison County, Homes

Homes in Madison County

Madison County is a place of houses on their own lots: 79% of its 118,942 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1970, close to Illinois' 1970: 37% date from before 1960 and 17% from 2000 or later. 74% 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 Madison County, Illinois, 2019 to 2023
HomesMadison CountyIllinois
Housing units118,9425,443,501
Detached houses79%58%
In buildings of 5 or more8%22%
Mobile homes2%2%
Built before 196037%38%
Built since 200017%16%
Middle year built19701970
Owner-occupied74%67%

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