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Radon Levels in Henry County, Illinois

EPA puts Henry County in Zone 1, its highest radon zone, and high results are common there: 55.7% of the 420 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

    55.7%

    22.0 pts above IL

    Henry
    55.7%
    Illinois
    33.7%

    420 tests, 2017

  • Median result

    4.6pCi/L

    Action level reached

    Henry
    4.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    420

    30th of 70 by tests

    Henry
    420
    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

    12 of 70

    Top quarter

    Henry
    55.7%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Henry County

Starts at Henry County's median, 4.6 pCi/L

4.6pCi/L

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

EPA’s reading of 4.6 pCi/L

At or above 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 at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Henry County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Henry County, At a glance

Henry County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Henry 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 Henry County, 2017

Share of reported tests at or above 4 pCi/L, by year, Henry County
Share of reported tests at or above 4 pCi/L, by year, Henry County
YearShare of reported tests at or above 4 pCi/L
201464.1%
201556.3%
2016100.0%
201755.7%

2017: 55.7%. Across these years the share ran from 55.7% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 420 tests reported to CDC for Henry 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

Henry County, Compared

Henry County radon figures, compared

Calculated by Radon411

More than half: 55.7% of the 420 radon tests reported to CDC for Henry County in 2017 read at least 4 pCi/L. That places it 12th of 70 Illinois counties with 30 or more tests for the same period. That is 22.0 points above the 33.7% pooled from 93 Illinois counties.

The median result, 4.6 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 39.2 pCi/L. The rest split 19.3% under 2 pCi/L and 25.0% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 55.7% share point the same way here.

4 of its 6 bordering counties with figures ran higher, led by Stark County at 69.2%; Whiteside County reported 43.1%. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).

The busiest year on file was 2014, with 786 tests reported; the quietest, 2016, had 9.

Over 3 years of annual figures the share fell 8.4 points, from 64.1% in 2014 to 55.7% in 2017; its peak was 64.1% in 2014. Nationally, every county with a figure for the same period pools to 31.7%; Henry County sits 24.0 points above it.

Share of reported tests at or above 4 pCi/L by year, Henry County against Illinois2014 to 2017, years with 30 or more tests: Henry County 64.1% to 55.7%, the state's pooled share 33.7% in 2017.
Henry CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Henry County against Illinois: data table
YearTestsHenry County, at or above 4 pCi/LIllinois, pooled
201478664.1%37.8%
201524056.3%36.6%
201742055.7%33.7%
Henry County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Henry County
Henry County42055.7%4.6 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−22.0 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−24.0 points
Morgan Countyhighest in the state38166.9%6.5 pCi/L+11.2 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−47.3 points
Stark County, ILborders it3969.2%5.8 pCi/L+13.5 points
Mercer County, ILborders it6668.2%5.5 pCi/L+12.5 points
Bureau County, ILborders it33358.6%5.1 pCi/L+2.9 points
Knox County, ILborders it24956.6%4.7 pCi/L+0.9 points
Rock Island County, ILborders it2,28346.5%3.7 pCi/L−9.2 points
Whiteside County, ILborders it69643.1%3.3 pCi/L−12.6 points
Where Henry County's reported results fell, 2017, beside Illinois and the United States
ResultHenry County testsHenry County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L8119.3%37.7%43.5%−18.4 points
2 to 4 pCi/L10525.0%28.6%24.8%−3.6 points
4 pCi/L and above23455.7%33.7%31.7%+22.0 points
Henry 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
Bureau County7 of 7033358.6%5.1 pCi/L
Stephenson County8 of 7051957.2%4.8 pCi/L
De Witt County9 of 7012657.1%5.2 pCi/L
Ford County9 of 704257.1%4.0 pCi/L
Knox County11 of 7024956.6%4.7 pCi/L
Henry County12 of 7042055.7%4.6 pCi/L
McDonough County12 of 7021055.7%4.3 pCi/L
Piatt County14 of 7027954.8%4.3 pCi/L
Vermilion County15 of 703953.8%4.7 pCi/L
Putnam County16 of 704553.3%4.5 pCi/L
Woodford County17 of 7076552.9%4.2 pCi/L
Henry County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201742055.7%4.6 pCi/L39.2 pCi/L33.7%−44.3 points
20169100.0%14.5 pCi/L14.6 pCi/L17.4%+43.7 points
201524056.3%4.7 pCi/L41.1 pCi/L36.6%−7.8 points
201478664.1%5.8 pCi/L36.2 pCi/L37.8%First on file

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

Henry County, Geology

The ground under Henry County

Predicted

USGS's geologic map puts all of Henry 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 Henry 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.

Henry County beside the ground around it

Henry 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; Knox County comes nearest at 100%.

Share of land by USGS radon potential: Henry County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Henry CountyZone 1NoneNone100%
Rock Island CountyZone 1NoneNone100%
Whiteside CountyZone 1NoneNone100%
Stark CountyZone 1NoneNone100%
Bureau CountyZone 1NoneNone100%
Mercer CountyZone 1NoneNone100%
Knox 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

Henry County, Local resources

Radon testing and mitigation in Henry County

Listed radon businesses with an address in Henry County:

Listed radon professionals by town: Kewanee, Geneseo, Orion

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

Henry County, Questions

Questions about radon in Henry County

Are radon levels high in Henry County?

In 2017, 55.7% of the radon tests reported to CDC for Henry County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.6 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 11 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Henry County?

Henry County borders 6 counties: Rock Island County, Whiteside County, Stark County, Bureau County, Mercer County and Knox County.

Products

Henry County, Products

Testing a home in Henry County

In Henry County, 55.7% of 420 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Henry 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

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

Explore

Henry County, Bordering counties

Counties bordering Henry County

Calculated by Radon411

Henry County, Cities and towns

Cities and towns in Henry County

About 48,095 people live in Henry County by the Census Bureau's estimate for July 1, 2025, 1,079 fewer than in 2020 (−2.2%). That works out to 58 people per square mile of land. Its largest town, Kewanee, has 12,115 residents, 25.2% of the total. CDC's 420 reported tests for 2017 work out to 8.7 per 1,000 residents (2025 estimate), close to Illinois' 10.9.

From Kewanee to Bishop Hill, CDC publishes no figure by town: each reads Henry County's.

The 12 largest cities and towns in Henry County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Kewanee12,115−2.8%25.2%
Geneseo6,505−0.5%13.5%
Colona4,938−1.7%10.3%
Coal Valleyextends beyond Henry County3,859−0.2%Counted whole
Galva2,383−3.0%5.0%
Cambridge2,020−2.8%4.2%
Orion1,708−2.5%3.6%
Atkinson924−3.0%1.9%
Annawanextends beyond Henry County858−2.9%Counted whole
Woodhull731−2.9%1.5%
Alpha653−2.7%1.4%
Andover536−3.1%1.1%
  • Hooppole
  • Cleveland
  • Bishop Hill

15 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 Henry County is counted whole, so it has no share.

Henry County, Homes

Homes in Henry County

Henry County is a place of houses on their own lots: 87% of its 22,208 homes are detached single-family houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1961 (1970 for Illinois), and 48% date from before 1960. Owners live in 80% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Henry County, Illinois, 2019 to 2023
HomesHenry CountyIllinois
Housing units22,2085,443,501
Detached houses87%58%
In buildings of 5 or more5%22%
Mobile homes2%2%
Built before 196048%38%
Built since 20008%16%
Middle year built19611970
Owner-occupied80%67%

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