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Radon Levels in Macon County, Illinois

EPA puts Macon County in Zone 1, its highest radon zone, and 38.8% of its 1,251 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

    38.8%

    5.1 pts above IL

    Macon
    38.8%
    Illinois
    33.7%

    1,251 tests, 2017

  • Median result

    3.1pCi/L

    Below action level

    Macon
    3.1 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    1,251

    18th of 70 by tests

    Macon
    1,251
    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

    44 of 70

    Middle half

    Macon
    38.8%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Macon County

Starts at Macon County's median, 3.1 pCi/L

3.1pCi/L

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

EPA’s reading of 3.1 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. Macon County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Macon County, At a glance

Macon County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Macon 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 Macon County, 2017

Share of reported tests at or above 4 pCi/L, by year, Macon County
Share of reported tests at or above 4 pCi/L, by year, Macon County
YearShare of reported tests at or above 4 pCi/L
201442.3%
201537.8%
201738.8%

2017: 38.8%. Across these years the share ran from 37.8% to 42.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 1,251 tests reported to CDC for Macon 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

Macon County, Compared

Macon County radon figures, compared

Calculated by Radon411

In Macon County, about 4 in 10 reported tests in 2017 (486 of 1,251) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 7.1 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Macon County runs 5.1 points above its state.

Of 6 neighbours with a figure, all 6 reported a larger share at or above 4 pCi/L; the spread is 42.3% (Christian County) to 57.1% (De Witt County). By share, Macon County is 44th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 42.3% and 2017 closed at 38.8% (down 3.5 points), with 2014 the high at 42.3%. Half the tests came in under 3.1 pCi/L and half over it; the single highest reached 23.1 pCi/L. Below the action level, 345 tests (27.6%) came in under 2 pCi/L, against 37.7% statewide, and 420 tests (33.6%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 38.8% 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 2,349 tests reported; the quietest, 2015, had 834.

Share of reported tests at or above 4 pCi/L by year, Macon County against Illinois2014 to 2017, years with 30 or more tests: Macon County 42.3% to 38.8%, the state's pooled share 33.7% in 2017.
Macon CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Macon County against Illinois: data table
YearTestsMacon County, at or above 4 pCi/LIllinois, pooled
20142,34942.3%37.8%
201583437.8%36.6%
20171,25138.8%33.7%
Macon County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Macon County
Macon County1,25138.8%3.1 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−5.1 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−7.1 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+30.4 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−30.4 points
Shelby County, ILborders it2171.4%5.2 pCi/L+32.6 points
De Witt County, ILborders it12657.1%5.2 pCi/L+18.3 points
Piatt County, ILborders it27954.8%4.3 pCi/L+16.0 points
Moultrie County, ILborders it4546.7%3.3 pCi/L+7.9 points
Logan County, ILborders it7245.8%3.4 pCi/L+7.0 points
Sangamon County, ILborders it3,37843.7%3.7 pCi/L+4.9 points
Christian County, ILborders it21342.3%3.5 pCi/L+3.5 points
Where Macon County's reported results fell, 2017, beside Illinois and the United States
ResultMacon County testsMacon County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L34527.6%37.7%43.5%−10.1 points
2 to 4 pCi/L42033.6%28.6%24.8%+5.0 points
4 pCi/L and above48638.8%33.7%31.7%+5.1 points
Macon 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
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
Macon County44 of 701,25138.8%3.1 pCi/L
Effingham County45 of 7014138.3%2.7 pCi/L
Clinton County46 of 7058237.6%3.0 pCi/L
Kane County47 of 708,68236.6%2.8 pCi/L
McHenry County48 of 706,47435.1%2.9 pCi/L
Randolph County49 of 706035.0%2.9 pCi/L
Macon County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20171,25138.8%3.1 pCi/L23.1 pCi/L33.7%+1.0 points
201583437.8%3.0 pCi/L21.4 pCi/L36.6%−4.5 points
20142,34942.3%3.2 pCi/L37.1 pCi/L37.8%First on file

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

Macon County, Geology

The ground under Macon County

Predicted

USGS's geologic map puts all of Macon County's mapped land in one class: high radon potential. The map puts 76.4% of Macon County in the area it calls Bloomington Ridged Plain and 23.6% in Galesburg Plain. USGS gives both a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Macon County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High1376.4%
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High1323.6%

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

Macon County beside the ground around it

Macon County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 7 counties that border it, none has as large a share of high-potential ground; De Witt County comes nearest at 100%.

Share of land by USGS radon potential: Macon County, the 7 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Macon CountyZone 1NoneNone100%
Piatt CountyZone 1NoneNone100%
De Witt CountyZone 1NoneNone100%
Moultrie CountyZone 1NoneNone100%
Christian CountyZone 2None16.9%83.1%
Logan CountyZone 1NoneNone100%
Shelby CountyZone 2None54.9%45.1%
Sangamon 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

Macon County, Local resources

Radon testing and mitigation in Macon County

Listed radon businesses with an address in Macon County:

Listed radon professionals by town: Decatur

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

Macon County, Questions

Questions about radon in Macon County

Are radon levels high in Macon County?

In 2017, 38.8% of the radon tests reported to CDC for Macon County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.1 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 43 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Macon County?

Macon County borders 7 counties: Piatt County, De Witt County, Moultrie County, Christian County, Logan County, Shelby County and Sangamon County.

Products

Macon County, Products

Testing a home in Macon County

In Macon County, 38.8% of 1,251 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Macon 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

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

Explore

Macon County, Bordering counties

Counties bordering Macon County

Calculated by Radon411

Macon County, Cities and towns

Cities and towns in Macon County

About 99,300 people live in Macon County by the Census Bureau's estimate for July 1, 2025, 4,461 fewer than in 2020 (−4.3%). That works out to 171 people per square mile of land. Decatur alone is home to 67,884 of them, 68.4% of the total. Together its 12 incorporated places hold 87.5% of those residents; the other 12.5% live outside any of them. CDC's 1,251 reported tests for 2017 work out to 12.6 per 1,000 residents (2025 estimate), close to Illinois' 10.9.

From Decatur to Niantic, CDC publishes no figure by town: each reads Macon County's.

The cities and towns in Macon County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Decatur67,884−4.7%68.4%
Mount Zion5,880−2.1%5.9%
Forsyth3,613−3.2%3.6%
Maroa1,517−4.0%1.5%
Harristown1,247−4.5%1.3%
Long Creek1,212−3.4%1.2%
Macon1,120−4.2%1.1%
Blue Mound1,078−4.5%1.1%
Warrensburg1,068−3.9%1.1%
Argenta872−4.5%0.9%
Oreana845−4.5%0.9%
Niantic578−5.1%0.6%

12 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).

Macon County, Homes

Homes in Macon County

Macon County is a place of houses on their own lots: 78% of its 49,699 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1964, close to Illinois' 1970: 45% date from before 1960 and 8% from 2000 or later. 70% 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 Macon County, Illinois, 2019 to 2023
HomesMacon CountyIllinois
Housing units49,6995,443,501
Detached houses78%58%
In buildings of 5 or more14%22%
Mobile homes2%2%
Built before 196045%38%
Built since 20008%16%
Middle year built19641970
Owner-occupied70%67%

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