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Radon Levels in Sangamon County, Illinois

EPA puts Sangamon County in Zone 1, its highest radon zone, and high results are common there: 43.7% of the 3,378 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

    43.7%

    10.0 pts above IL

    Sangamon
    43.7%
    Illinois
    33.7%

    3,378 tests, 2017

  • Median result

    3.7pCi/L

    Below action level

    Sangamon
    3.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    3,378

    11th of 70 by tests

    Sangamon
    3,378
    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

    36 of 70

    Middle half

    Sangamon
    43.7%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Sangamon County

Starts at Sangamon County's median, 3.7 pCi/L

3.7pCi/L

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

EPA’s reading of 3.7 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. Sangamon County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Sangamon County, At a glance

Sangamon County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Sangamon 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 Sangamon County, 2017

Share of reported tests at or above 4 pCi/L, by year, Sangamon County
Share of reported tests at or above 4 pCi/L, by year, Sangamon County
YearShare of reported tests at or above 4 pCi/L
201449.3%
201548.8%
201666.7%
201743.7%

2017: 43.7%. Across these years the share ran from 43.7% to 66.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 3,378 tests reported to CDC for Sangamon 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

Sangamon County, Compared

Sangamon County radon figures, compared

Calculated by Radon411

In Sangamon County, about 4 in 10 reported tests in 2017 (1,476 of 3,378) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 12.0 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Sangamon County runs 10.0 points above its state.

Of 7 neighbours with a figure, 4 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 25.6% (Macoupin County) to 66.9% (Morgan County). By share, Sangamon County is 36th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 49.3% and 2017 closed at 43.7% (down 5.6 points), with 2014 the high at 49.3%. Half the tests came in under 3.7 pCi/L and half over it; the single highest reached 64.4 pCi/L. Below the action level, 738 tests (21.8%) came in under 2 pCi/L, against 37.7% statewide, and 1,164 tests (34.5%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 43.7% 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 5,307 tests reported; the quietest, 2016, had 18.

Share of reported tests at or above 4 pCi/L by year, Sangamon County against Illinois2014 to 2017, years with 30 or more tests: Sangamon County 49.3% to 43.7%, the state's pooled share 33.7% in 2017.
Sangamon CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Sangamon County against Illinois: data table
YearTestsSangamon County, at or above 4 pCi/LIllinois, pooled
20145,30749.3%37.8%
20152,73648.8%36.6%
20173,37843.7%33.7%
Sangamon County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Sangamon County
Sangamon County3,37843.7%3.7 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−10.0 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−12.0 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+25.5 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−35.3 points
Morgan County, ILborders it38166.9%6.5 pCi/L+23.2 points
Menard County, ILborders it16851.8%4.3 pCi/L+8.1 points
Logan County, ILborders it7245.8%3.4 pCi/L+2.1 points
Montgomery County, ILborders it12343.9%3.3 pCi/L+0.2 points
Christian County, ILborders it21342.3%3.5 pCi/L−1.4 points
Macon County, ILborders it1,25138.8%3.1 pCi/L−4.9 points
Macoupin County, ILborders it25825.6%2.2 pCi/L−18.1 points
Cass County, ILborders it2425.0%2.9 pCi/L−18.7 points
Where Sangamon County's reported results fell, 2017, beside Illinois and the United States
ResultSangamon County testsSangamon County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L73821.8%37.7%43.5%−15.9 points
2 to 4 pCi/L1,16434.5%28.6%24.8%+5.9 points
4 pCi/L and above1,47643.7%33.7%31.7%+10.0 points
Sangamon 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
LaSalle County31 of 701,00245.8%3.6 pCi/L
Jo Daviess County32 of 7051345.0%3.5 pCi/L
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
Sangamon County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20173,37843.7%3.7 pCi/L64.4 pCi/L33.7%−23.0 points
20161866.7%5.3 pCi/L7.9 pCi/L17.4%+17.9 points
20152,73648.8%3.9 pCi/L831.0 pCi/L36.6%−0.5 points
20145,30749.3%3.9 pCi/L31.8 pCi/L37.8%First on file

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

Sangamon County, Geology

The ground under Sangamon County

Predicted

USGS's geologic map puts all of Sangamon County's mapped land in one class: high radon potential. All of it lies in the area the map calls Galesburg Plain, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Sangamon County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Galesburg PlainIllinoian 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.

Sangamon County beside the ground around it

Sangamon 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; Cass County comes nearest at 100%.

Share of land by USGS radon potential: Sangamon County, the 8 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Sangamon CountyZone 1NoneNone100%
Menard CountyZone 1NoneNone100%
Morgan CountyZone 1NoneNone100%
Christian CountyZone 2None16.9%83.1%
Logan CountyZone 1NoneNone100%
Cass CountyZone 1NoneNone100%
Montgomery CountyZone 2None88.8%11.2%
Macon CountyZone 1NoneNone100%
Macoupin CountyZone 2None42.4%57.6%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Sangamon County, Local resources

Radon testing and mitigation in Sangamon County

Listed radon businesses with an address in Sangamon County:

Listed radon professionals by town: Springfield, Rochester

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

Sangamon County, Questions

Questions about radon in Sangamon County

Are radon levels high in Sangamon County?

In 2017, 43.7% of the radon tests reported to CDC for Sangamon County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.7 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 35 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Sangamon County?

Sangamon County borders 8 counties: Menard County, Morgan County, Christian County, Logan County, Cass County, Montgomery County, Macon County and Macoupin County.

Products

Sangamon County, Products

Testing a home in Sangamon County

In Sangamon County, 43.7% of 3,378 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Sangamon 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

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

Explore

Sangamon County, Bordering counties

Counties bordering Sangamon County

Calculated by Radon411

Sangamon County, Cities and towns

Cities and towns in Sangamon County

About 194,170 people live in Sangamon County by the Census Bureau's estimate for July 1, 2025, 2,032 fewer than in 2020 (−1.0%). That works out to 224 people per square mile of land. Springfield alone is home to 112,989 of them, 58.2% of the total. Testing is reported here more often than across the state: CDC's 3,378 reported tests for 2017 come to 17.4 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.

From Springfield to Clear Lake, CDC publishes no figure by town: each reads Sangamon County's.

The 12 largest cities and towns in Sangamon County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Springfield112,989−1.3%58.2%
Chatham14,579+1.1%7.5%
Sherman4,644−0.6%2.4%
Auburn4,442−2.2%2.3%
Rochester4,093+6.0%2.1%
Riverton3,471−2.2%1.8%
Virdenextends beyond Sangamon County3,149−2.4%Counted whole
Pawnee2,686+0.2%1.4%
Jerome1,627−2.8%0.8%
Southern View1,540−2.8%0.8%
Williamsville1,437−0.1%0.7%
Leland Grove1,401−2.9%0.7%
  • Grandview
  • New Berlin
  • Divernon
  • Illiopolis
  • Pleasant Plains
  • Loami
  • Spaulding
  • Mechanicsburg
  • Thayer
  • Dawson
  • Buffalo
  • Curran
  • Berlin
  • Cantrall
  • Clear Lake

27 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 Sangamon County is counted whole, so it has no share.

Sangamon County, Homes

Homes in Sangamon County

Of Sangamon County's 93,151 homes, 73% are detached houses, against 58% across Illinois; 12% are in buildings of five or more homes. Half of its homes were built before 1973, close to Illinois' 1970: 33% date from before 1960 and 15% from 2000 or later. 71% 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 Sangamon County, Illinois, 2019 to 2023
HomesSangamon CountyIllinois
Housing units93,1515,443,501
Detached houses73%58%
In buildings of 5 or more12%22%
Mobile homes4%2%
Built before 196033%38%
Built since 200015%16%
Middle year built19731970
Owner-occupied71%67%

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