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Radon Levels in Boone County, Illinois

EPA puts Boone County in Zone 1, its highest radon zone, and high results are common there: 46.9% of the 525 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

    46.9%

    13.2 pts above IL

    Boone
    46.9%
    Illinois
    33.7%

    525 tests, 2017

  • Median result

    3.4pCi/L

    Below action level

    Boone
    3.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    525

    26th of 70 by tests

    Boone
    525
    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

    24 of 70

    Middle half

    Boone
    46.9%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Boone County

Starts at Boone County's median, 3.4 pCi/L

3.4pCi/L

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

EPA’s reading of 3.4 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. Boone County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Boone County, At a glance

Boone County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Boone 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 Boone County, 2017

Share of reported tests at or above 4 pCi/L, by year, Boone County
Share of reported tests at or above 4 pCi/L, by year, Boone County
YearShare of reported tests at or above 4 pCi/L
201455.1%
201544.8%
2016100.0%
201746.9%

2017: 46.9%. Across these years the share ran from 44.8% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 525 tests reported to CDC for Boone 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

Boone County, Compared

Boone County radon figures, compared

Calculated by Radon411

In Boone County, about 5 in 10 reported tests in 2017 (246 of 525) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 15.2 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Boone County runs 13.2 points above its state.

Of 6 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 34.9% (Winnebago County) to 56.8% (Rock County, WI). By share, Boone County is 24th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 55.1% and 2017 closed at 46.9% (down 8.2 points), with 2014 the high at 55.1%. Half the tests came in under 3.4 pCi/L and half over it; the single highest reached 28.3 pCi/L. Below the action level, 147 tests (28.0%) came in under 2 pCi/L, against 37.7% statewide, and 132 tests (25.1%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 46.9% 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 681 tests reported; the quietest, 2016, had 3.

Share of reported tests at or above 4 pCi/L by year, Boone County against Illinois2014 to 2017, years with 30 or more tests: Boone County 55.1% to 46.9%, the state's pooled share 33.7% in 2017.
Boone CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Boone County against Illinois: data table
YearTestsBoone County, at or above 4 pCi/LIllinois, pooled
201468155.1%37.8%
201537544.8%36.6%
201752546.9%33.7%
Boone County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Boone County
Boone County52546.9%3.4 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−13.2 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−15.2 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+22.3 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−38.5 points
Rock County, WIborders it36156.8%4.6 pCi/L+9.9 points
Walworth County, WIborders it23456.0%4.5 pCi/L+9.1 points
Ogle County, ILborders it63652.4%4.1 pCi/L+5.5 points
DeKalb County, ILborders it1,70741.1%3.3 pCi/L−5.8 points
McHenry County, ILborders it6,47435.1%2.9 pCi/L−11.8 points
Winnebago County, ILborders it2,70334.9%2.9 pCi/L−12.0 points
Where Boone County's reported results fell, 2017, beside Illinois and the United States
ResultBoone County testsBoone County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L14728.0%37.7%43.5%−9.7 points
2 to 4 pCi/L13225.1%28.6%24.8%−3.5 points
4 pCi/L and above24646.9%33.7%31.7%+13.2 points
Boone 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
Menard County19 of 7016851.8%4.3 pCi/L
Coles County20 of 7019851.5%4.2 pCi/L
Douglas County21 of 708450.0%3.8 pCi/L
Warren County21 of 704250.0%3.6 pCi/L
Marshall County23 of 708148.1%3.8 pCi/L
Boone County24 of 7052546.9%3.4 pCi/L
Moultrie County25 of 704546.7%3.3 pCi/L
Rock Island County26 of 702,28346.5%3.7 pCi/L
Jersey County27 of 7012946.5%3.6 pCi/L
Tazewell County28 of 702,72446.4%3.6 pCi/L
Adams County29 of 7088546.1%3.6 pCi/L
Boone County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201752546.9%3.4 pCi/L28.3 pCi/L33.7%−53.1 points
20163100.0%5.9 pCi/L5.9 pCi/L17.4%+55.2 points
201537544.8%3.4 pCi/L30.1 pCi/L36.6%−10.3 points
201468155.1%4.5 pCi/L20.5 pCi/L37.8%First on file

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

Boone County, Geology

The ground under Boone County

Predicted

USGS's geologic map puts all of Boone 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 Boone 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.

Boone County beside the ground around it

Boone County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 6 counties that border it, none has as large a share of high-potential ground; DeKalb County comes nearest at 100%.

Share of land by USGS radon potential: Boone County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Boone CountyZone 1NoneNone100%
Winnebago CountyZone 1NoneNone100%
McHenry CountyZone 2NoneNone100%
Rock County, WIZone 1NoneNone100%
Walworth County, WIZone 1NoneNone100%
Ogle CountyZone 1NoneNone100%
DeKalb 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

Boone County, Local resources

Radon testing and mitigation in Boone County

Listed radon businesses with an address in Boone County:

Listed radon professionals by town: Poplar Grove

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

Boone County, Questions

Questions about radon in Boone County

Are radon levels high in Boone County?

In 2017, 46.9% of the radon tests reported to CDC for Boone County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.4 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 23 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Boone County?

Boone County borders 6 counties: Winnebago County, IL, McHenry County, IL, Rock County, WI, Walworth County, WI, Ogle County, IL and DeKalb County, IL.

Products

Boone County, Products

Testing a home in Boone County

In Boone County, 46.9% of 525 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Boone 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

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

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Boone County, Bordering counties

Counties bordering Boone County

Calculated by Radon411

Boone County, Cities and towns

Cities and towns in Boone County

Boone County's population has barely moved since 2020: 53,568 residents on July 1, 2025 against 53,344 then, by the Census Bureau's estimates. That works out to 191 people per square mile of land. Its largest town, Belvidere, has 25,462 residents, 47.5% of the total. CDC's 525 reported tests for 2017 work out to 9.8 per 1,000 residents (2025 estimate), close to Illinois' 10.9.

From Belvidere to Caledonia, CDC publishes no figure by town: each reads Boone County's.

The cities and towns in Boone County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Belvidere25,462+0.7%47.5%
Loves Parkextends beyond Boone County23,712+1.2%Counted whole
Poplar Grove5,206+2.9%9.7%
Cherry Valleyextends beyond Boone County2,887+0.2%Counted whole
Capron1,407+1.4%2.6%
Timberlane908+0.3%1.7%
Caledonia183−0.5%0.3%

7 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). A place that extends beyond Boone County is counted whole, so it has no share.

Boone County, Homes

Homes in Boone County

Boone County is a place of houses on their own lots: 80% of its 20,238 homes are detached single-family houses, against 58% across Illinois. Much of Boone County is recent building: 25% of its homes have gone up since 2000 and the middle year built is 1981, against 1970 for Illinois. Owners live in 83% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Boone County, Illinois, 2019 to 2023
HomesBoone CountyIllinois
Housing units20,2385,443,501
Detached houses80%58%
In buildings of 5 or more3%22%
Mobile homes6%2%
Built before 196028%38%
Built since 200025%16%
Middle year built19811970
Owner-occupied83%67%

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