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Radon Levels in DeKalb County, Illinois

EPA puts DeKalb County in Zone 1, its highest radon zone, and high results are common there: 41.1% of the 1,707 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

    41.1%

    7.4 pts above IL

    DeKalb
    41.1%
    Illinois
    33.7%

    1,707 tests, 2017

  • Median result

    3.3pCi/L

    Below action level

    DeKalb
    3.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    1,707

    17th of 70 by tests

    DeKalb
    1,707
    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

    40 of 70

    Middle half

    DeKalb
    41.1%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for DeKalb County

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

Interpret this readingWhat a fix costs

The data

DeKalb County, At a glance

DeKalb County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of DeKalb 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 DeKalb County, 2017

Share of reported tests at or above 4 pCi/L, by year, DeKalb County
Share of reported tests at or above 4 pCi/L, by year, DeKalb County
YearShare of reported tests at or above 4 pCi/L
201448.9%
201546.1%
201628.6%
201741.1%

2017: 41.1%. Across these years the share ran from 28.6% to 48.9%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 1,707 tests reported to CDC for DeKalb 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

DeKalb County, Compared

DeKalb County radon figures, compared

Calculated by Radon411

In DeKalb County, about 4 in 10 reported tests in 2017 (702 of 1,707) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 9.4 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so DeKalb County runs 7.4 points above its state.

Of 8 neighbours with a figure, 4 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 34.9% (Winnebago County) to 52.4% (Ogle County). By share, DeKalb County is 40th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 48.9% and 2017 closed at 41.1% (down 7.8 points), with 2014 the high at 48.9%. Half the tests came in under 3.3 pCi/L and half over it; the single highest reached 41.9 pCi/L. Below the action level, 561 tests (32.9%) came in under 2 pCi/L, against 37.7% statewide, and 444 tests (26.0%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 41.1% 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 1,962 tests reported; the quietest, 2016, had 21.

Share of reported tests at or above 4 pCi/L by year, DeKalb County against Illinois2014 to 2017, years with 30 or more tests: DeKalb County 48.9% to 41.1%, the state's pooled share 33.7% in 2017.
DeKalb CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, DeKalb County against Illinois: data table
YearTestsDeKalb County, at or above 4 pCi/LIllinois, pooled
20141,96248.9%37.8%
201569046.1%36.6%
20171,70741.1%33.7%
DeKalb County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from DeKalb County
DeKalb County1,70741.1%3.3 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−7.4 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−9.4 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+28.1 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−32.7 points
Ogle County, ILborders it63652.4%4.1 pCi/L+11.3 points
Boone County, ILborders it52546.9%3.4 pCi/L+5.8 points
LaSalle County, ILborders it1,00245.8%3.6 pCi/L+4.7 points
Lee County, ILborders it21943.8%3.3 pCi/L+2.7 points
Kane County, ILborders it8,68236.6%2.8 pCi/L−4.5 points
McHenry County, ILborders it6,47435.1%2.9 pCi/L−6.0 points
Kendall County, ILborders it3,04535.0%2.8 pCi/L−6.1 points
Winnebago County, ILborders it2,70334.9%2.9 pCi/L−6.2 points
Where DeKalb County's reported results fell, 2017, beside Illinois and the United States
ResultDeKalb County testsDeKalb County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L56132.9%37.7%43.5%−4.8 points
2 to 4 pCi/L44426.0%28.6%24.8%−2.6 points
4 pCi/L and above70241.1%33.7%31.7%+7.4 points
DeKalb 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
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
Macon County44 of 701,25138.8%3.1 pCi/L
Effingham County45 of 7014138.3%2.7 pCi/L
DeKalb County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20171,70741.1%3.3 pCi/L41.9 pCi/L33.7%+12.5 points
20162128.6%2.3 pCi/L5.4 pCi/L17.4%−17.5 points
201569046.1%3.7 pCi/L128.8 pCi/L36.6%−2.8 points
20141,96248.9%3.8 pCi/L90.6 pCi/L37.8%First on file

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

DeKalb County, Geology

The ground under DeKalb County

Predicted

USGS's geologic map puts all of DeKalb County's mapped land in one class: high radon potential. The map puts 90.3% of DeKalb County in the area it calls Bloomington Ridged Plain and 9.7% in Galesburg Plain. USGS gives both a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under DeKalb County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High1390.3%
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High139.7%

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

DeKalb County beside the ground around it

DeKalb 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; Boone County comes nearest at 100%.

Share of land by USGS radon potential: DeKalb County, the 8 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
DeKalb CountyZone 1NoneNone100%
Kane CountyZone 1NoneNone100%
Kendall CountyZone 1NoneNone100%
Lee CountyZone 1NoneNone100%
Ogle CountyZone 1NoneNone100%
Boone CountyZone 1NoneNone100%
McHenry CountyZone 2NoneNone100%
LaSalle CountyZone 1NoneNone100%
Winnebago 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

DeKalb County, Local resources

Radon testing and mitigation in DeKalb County

Listed radon businesses with an address in DeKalb County:

Listed radon professionals by town: Sycamore

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

DeKalb County, Questions

Questions about radon in DeKalb County

Are radon levels high in DeKalb County?

In 2017, 41.1% of the radon tests reported to CDC for DeKalb 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, 39 reported a higher share; pooled, the state comes to 33.7%.

Which counties border DeKalb County?

DeKalb County borders 8 counties: Kane County, Kendall County, Lee County, Ogle County, Boone County, McHenry County, LaSalle County and Winnebago County.

Products

DeKalb County, Products

Testing a home in DeKalb County

In DeKalb County, 41.1% of 1,707 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in DeKalb 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

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

Explore

DeKalb County, Bordering counties

Counties bordering DeKalb County

Calculated by Radon411

DeKalb County, Cities and towns

Cities and towns in DeKalb County

The Census Bureau estimates 101,835 residents in DeKalb County for July 1, 2025, 1,469 more than in 2020 (+1.5%). That works out to 161 people per square mile of land. Its largest town, DeKalb, has 40,467 residents, 39.7% of the total. Testing is reported here more often than across the state: CDC's 1,707 reported tests for 2017 come to 16.8 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.

From DeKalb to Lee, CDC publishes no figure by town: each reads DeKalb County's.

The 12 largest cities and towns in DeKalb County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
DeKalb40,467+0.6%39.7%
Sycamore19,083+2.3%18.7%
Sandwichextends beyond DeKalb County7,380+2.3%Counted whole
Genoa5,547+4.6%5.4%
Cortland4,676+6.4%4.6%
Hinckley1,996−0.1%2.0%
Somonaukextends beyond DeKalb County1,770−1.2%Counted whole
Waterman1,640+14.6%1.6%
Kirkland1,632−1.2%1.6%
Maple Parkextends beyond DeKalb County1,523+6.3%Counted whole
Malta1,140−0.3%1.1%
Kingston1,103−0.5%1.1%
  • Shabbona
  • Lee (part)

14 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 DeKalb County is counted whole, so it has no share.

DeKalb County, Homes

Homes in DeKalb County

Of DeKalb County's 41,499 homes, 57% are detached houses, against 58% across Illinois; 22% are in buildings of five or more homes. Much of DeKalb County is recent building: 26% of its homes have gone up since 2000 and the middle year built is 1978, against 1970 for Illinois. 61% 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 DeKalb County, Illinois, 2019 to 2023
HomesDeKalb CountyIllinois
Housing units41,4995,443,501
Detached houses57%58%
In buildings of 5 or more22%22%
Mobile homes2%2%
Built before 196026%38%
Built since 200026%16%
Middle year built19781970
Owner-occupied61%67%

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