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Radon Levels in Henderson County, Illinois

EPA puts Henderson County in Zone 1, its highest radon zone, and only 3 radon tests from it are on file with CDC (2015). Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Share at 4+ pCi/L

    68.4%

    25.3 pts above IL

    Henderson
    68.4%
    Illinois
    43.1%

    38 tests, 2008 to 2017

  • Median result

    5.7pCi/L

    Action level reached

    Henderson
    5.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    38

    88th of 93 by tests

    Henderson
    38
    Cook
    14,199

    Reported to CDC before any fix, 2008 to 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

    3 of 93

    Top quarter

    Henderson
    68.4%
    Stark
    80.5%

    By share, of 93 with 30+ tests

Read a result for Henderson County

Starts at Henderson County's median, 5.7 pCi/L

5.7pCi/L

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

EPA’s reading of 5.7 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. Henderson County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Henderson County, At a glance

Henderson County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Henderson 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 Henderson County, 2015

Share of reported tests at or above 4 pCi/L, by year, Henderson County
Share of reported tests at or above 4 pCi/L, by year, Henderson County
YearShare of reported tests at or above 4 pCi/L
201466.7%
20150.0%

2015: 0.0%. Across these years the share ran from 0.0% to 66.7%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 3 tests were reported to CDC for Henderson County over 2015, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.

Measured: CDC tracking data. Figure above: 2015. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Henderson County, Compared

Henderson County radon figures, compared

Calculated by Radon411

More than half: 68.4% of the 38 radon tests reported to CDC for Henderson County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 3rd of 93 Illinois counties with 30 or more tests for the same period. That is 25.3 points above the 43.1% pooled from 102 Illinois counties.

The newest figure, in 2015, counts only 3 tests (0.0% at or above 4 pCi/L), too few to compare, so this reading uses the 38-test figure.

The median result, 5.7 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 32.7 pCi/L. The rest split 15.8% under 2 pCi/L and 15.8% from 2 to 4 (Illinois: 31.6% and 25.3%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 68.4% share point the same way here.

1 of its 6 bordering counties with figures ran higher, led by Warren County at 75.3%; Hancock County reported 43.5%. Statewide for the same period, Stark County reported the highest share (80.5%) and Williamson County the lowest (13.3%).

The busiest year on file was 2014, with 18 tests reported; the quietest, 2015, had 3.

Nationally, every county with a figure for the same period pools to 35.7%; Henderson County sits 32.7 points above it.

Henderson County against Illinois, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Henderson County
Henderson County3868.4%5.7 pCi/LThis county
Illinois, pooled102 counties, pooled108,90943.1%Not pooled−25.3 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−32.7 points
Stark Countyhighest in the state8780.5%7.4 pCi/L+12.1 points
Williamson Countylowest in the state60113.3%1.3 pCi/L−55.1 points
Warren County, ILborders it30475.3%7.1 pCi/L+6.9 points
Mercer County, ILborders it34367.1%6.8 pCi/L−1.3 points
McDonough County, ILborders it72054.4%4.5 pCi/L−14.0 points
Des Moines County, IAborders it43651.1%4.2 pCi/L−17.3 points
Lee County, IAborders it35143.6%3.2 pCi/L−24.8 points
Hancock County, ILborders it17743.5%3.5 pCi/L−24.9 points
Where Henderson County's reported results fell, 2008 to 2017, laboratory, beside Illinois and the United States
ResultHenderson County testsHenderson County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L615.8%31.6%39.6%−15.8 points
2 to 4 pCi/L615.8%25.3%24.7%−9.5 points
4 pCi/L and above2668.4%43.1%35.7%+25.3 points
Henderson County ranked among the 93 Illinois counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Stark County1 of 938780.5%7.4 pCi/L
Warren County2 of 9330475.3%7.1 pCi/L
Henderson County3 of 933868.4%5.7 pCi/L
Mercer County4 of 9334367.1%6.8 pCi/L
Knox County5 of 9385365.9%6.1 pCi/L
Morgan County6 of 9316964.5%5.8 pCi/L
Fulton County7 of 9332964.4%5.4 pCi/L
Marshall County8 of 9320563.9%6.0 pCi/L
Stephenson County9 of 931,21763.2%5.3 pCi/L
Ogle County10 of 9381662.5%5.5 pCi/L
Logan County11 of 9339062.1%5.3 pCi/L
Henderson County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201530.0%3.4 pCi/L3.4 pCi/L36.6%−66.7 points
20141866.7%6.8 pCi/L17.3 pCi/L37.8%First on file

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

Henderson County, Geology

The ground under Henderson County

Predicted

USGS's geologic map puts all of Henderson 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 Henderson County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High1399.6%

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

Henderson County beside the ground around it

Henderson 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; Des Moines County, IA comes nearest at 100%.

Share of land by USGS radon potential: Henderson County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Henderson CountyZone 1NoneNone100%
Des Moines County, IAZone 1NoneNone100%
Warren CountyZone 1NoneNone100%
Mercer CountyZone 1NoneNone100%
McDonough CountyZone 1NoneNone100%
Hancock CountyZone 1NoneNone100%
Lee County, IAZone 1None0.1%99.9%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Henderson County, Local resources

Radon testing and mitigation in Henderson County

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

Henderson County, Questions

Questions about radon in Henderson County

Are radon levels high in Henderson County?

In 2015, 0.0% of the radon tests reported to CDC for Henderson County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.4 pCi/L. Of 93 Illinois counties with 30 or more tests for the same period, 2 reported a higher share; pooled, the state comes to 43.1%.

Which counties border Henderson County?

Henderson County borders 6 counties: Des Moines County, IA, Warren County, IL, Mercer County, IL, McDonough County, IL, Hancock County, IL and Lee County, IA.

Products

Henderson County, Products

Testing a home in Henderson County

In Henderson County, 68.4% of 38 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 43.1% pooled across Illinois. In Zone 1 the year-round level in Henderson 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

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

Explore

Henderson County, Bordering counties

Counties bordering Henderson County

Calculated by Radon411

Henderson County, Cities and towns

Cities and towns in Henderson County

Henderson County has been losing residents: from 6,340 in 2020 to 5,984 on July 1, 2025, a fall of 5.6% by the Census Bureau's estimates. That works out to 16 people per square mile of land. No town dominates: Oquawka, the largest, has 1,065 residents, 17.8% of the total. CDC's 38 reported tests for 2008 to 2017 work out to 6.4 per 1,000 residents (2025 estimate), close to Illinois' 8.6.

From Oquawka to Gulfport, CDC publishes no figure by town: each reads Henderson County's.

The 8 largest cities and towns in Henderson County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Oquawka1,065−5.7%17.8%
Dallas Cityextends beyond Henderson County767−5.0%Counted whole
Stronghurst760−6.3%12.7%
Lomax376−6.7%6.3%
Biggsville282−6.6%4.7%
Gladstone218−6.0%3.6%
Media110−7.6%1.8%
Raritan98−5.8%1.6%
  • Gulfport

9 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 Henderson County is counted whole, so it has no share.

Henderson County, Homes

Homes in Henderson County

Henderson County is a place of houses on their own lots: 84% of its 3,374 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1973, close to Illinois' 1970: 34% date from before 1960 and 10% from 2000 or later. Owners live in 86% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Henderson County, Illinois, 2019 to 2023
HomesHenderson CountyIllinois
Housing units3,3745,443,501
Detached houses84%58%
In buildings of 5 or more1%22%
Mobile homes13%2%
Built before 196034%38%
Built since 200010%16%
Middle year built19731970
Owner-occupied86%67%

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