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Radon Levels in Adams County, Illinois

EPA puts Adams County in Zone 1, its highest radon zone, and high results are common there: 46.1% of the 885 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

    46.1%

    12.4 pts above IL

    Adams
    46.1%
    Illinois
    33.7%

    885 tests, 2017

  • Median result

    3.6pCi/L

    Below action level

    Adams
    3.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    885

    20th of 70 by tests

    Adams
    885
    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

    29 of 70

    Middle half

    Adams
    46.1%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Adams County

Starts at Adams County's median, 3.6 pCi/L

3.6pCi/L

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

EPA’s reading of 3.6 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. Adams County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Adams County, At a glance

Adams County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Adams 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 Adams County, 2017

Share of reported tests at or above 4 pCi/L, by year, Adams County
Share of reported tests at or above 4 pCi/L, by year, Adams County
YearShare of reported tests at or above 4 pCi/L
201460.5%
201533.3%
201746.1%

2017: 46.1%. Across these years the share ran from 33.3% to 60.5%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 885 tests reported to CDC for Adams 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

Adams County, Compared

Adams County radon figures, compared

Calculated by Radon411

In Adams County, about 5 in 10 reported tests in 2017 (408 of 885) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 14.4 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Adams County runs 12.4 points above its state.

Hancock County, the one bordering county with a figure for the same period, reported 33.3%. By share, Adams County is 29th of 70 Illinois counties with 30 or more tests for the same period.

Half the tests came in under 3.6 pCi/L and half over it; the single highest reached 103.6 pCi/L. Below the action level, 210 tests (23.7%) came in under 2 pCi/L, against 37.7% statewide, and 267 tests (30.2%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 46.1% 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 2,310 tests reported; the quietest, 2015, had 9.

Adams County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Adams County
Adams County88546.1%3.6 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−12.4 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−14.4 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+23.1 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−37.7 points
Brown County, ILborders it1850.0%4.0 pCi/L+3.9 points
Marion County, MOborders it540.0%3.1 pCi/L−6.1 points
Hancock County, ILborders it6333.3%2.8 pCi/L−12.8 points
Pike County, ILborders it1225.0%2.8 pCi/L−21.1 points
Lewis County, MOborders it425.0%1.4 pCi/L−21.1 points
Where Adams County's reported results fell, 2017, beside Illinois and the United States
ResultAdams County testsAdams County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L21023.7%37.7%43.5%−14.0 points
2 to 4 pCi/L26730.2%28.6%24.8%+1.6 points
4 pCi/L and above40846.1%33.7%31.7%+12.4 points
Adams 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
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
Logan County30 of 707245.8%3.4 pCi/L
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
Adams County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201788546.1%3.6 pCi/L103.6 pCi/L33.7%+12.8 points
2015933.3%2.6 pCi/L24.6 pCi/L36.6%−27.2 points
20142,31060.5%5.1 pCi/L32.9 pCi/L37.8%First on file

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

Adams County, Geology

The ground under Adams County

Predicted

Most of the ground under Adams County is one class on USGS's geologic map: 99.9% of its land is high radon potential, with 0.1% moderate. 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 Adams County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High1399.9%

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

Adams County beside the ground around it

Adams County has more high-potential ground than Illinois as a whole: 99.9% of its land against 64.5%. Of the 6 counties that border it, 3 have more high-potential ground, Brown County the most at 100%.

Share of land by USGS radon potential: Adams County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Adams CountyZone 1None0.1%99.9%
Brown CountyZone 1NoneNone100%
Marion County, MOZone 2None98.5%1.5%
Pike CountyZone 1None0.1%99.9%
Hancock CountyZone 1NoneNone100%
Lewis County, MOZone 2None90.9%9.1%
Schuyler 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

Adams County, Local resources

Radon testing and mitigation in Adams County

Listed radon businesses with an address in Adams County:

Listed radon professionals by town: Camp Point

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

Adams County, Questions

Questions about radon in Adams County

Are radon levels high in Adams County?

In 2017, 46.1% of the radon tests reported to CDC for Adams County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.6 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Adams County?

Adams County borders 6 counties: Brown County, IL, Marion County, MO, Pike County, IL, Hancock County, IL, Lewis County, MO and Schuyler County, IL.

Products

Adams County, Products

Testing a home in Adams County

In Adams County, 46.1% of 885 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Adams 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

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

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Adams County, Bordering counties

Counties bordering Adams County

Calculated by Radon411

Adams County, Cities and towns

Cities and towns in Adams County

About 64,267 people live in Adams County by the Census Bureau's estimate for July 1, 2025, 1,370 fewer than in 2020 (−2.1%). That works out to 75 people per square mile of land. Quincy alone is home to 38,918 of them, 60.6% of the total. Together its 14 incorporated places hold 70.4% of those residents; the other 29.6% live outside any of them. CDC's 885 reported tests for 2017 work out to 13.8 per 1,000 residents (2025 estimate), close to Illinois' 10.9.

From Quincy to La Prairie, CDC publishes no figure by town: each reads Adams County's.

The 12 largest cities and towns in Adams County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Quincy38,918−1.6%60.6%
Camp Point1,119−0.6%1.7%
Payson994−2.9%1.5%
Mendon844−2.9%1.3%
Golden629−3.4%1.0%
Clayton616−3.3%1.0%
Ursa603−3.1%0.9%
Liberty522−3.2%0.8%
Loraine289−2.7%0.4%
Plainville260−3.3%0.4%
Coatsburg151−2.6%0.2%
Lima151−2.6%0.2%
  • Columbus
  • La Prairie

14 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).

Adams County, Homes

Homes in Adams County

Adams County is a place of houses on their own lots: 76% of its 30,283 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 13% from 2000 or later. 72% 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 Adams County, Illinois, 2019 to 2023
HomesAdams CountyIllinois
Housing units30,2835,443,501
Detached houses76%58%
In buildings of 5 or more9%22%
Mobile homes5%2%
Built before 196045%38%
Built since 200013%16%
Middle year built19641970
Owner-occupied72%67%

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