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Radon Levels in Montgomery County, Illinois

EPA puts Montgomery County in Zone 2, its middle radon zone, and high results are common there: 43.9% of the 123 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

    43.9%

    10.2 pts above IL

    Montgomery
    43.9%
    Illinois
    33.7%

    123 tests, 2017

  • Median result

    3.3pCi/L

    Below action level

    Montgomery
    3.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    123

    50th of 70 by tests

    Montgomery
    123
    Cook
    26,937

    Reported to CDC before any fix, 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in Illinois

    34 of 70

    Middle half

    Montgomery
    43.9%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Montgomery County

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

Interpret this readingWhat a fix costs

The data

Montgomery County, At a glance

Montgomery County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Montgomery County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

USGS geologic potential: Moderate across 89% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Montgomery County, 2017

Share of reported tests at or above 4 pCi/L, by year, Montgomery County
Share of reported tests at or above 4 pCi/L, by year, Montgomery County
YearShare of reported tests at or above 4 pCi/L
201428.6%
201534.8%
201743.9%

2017: 43.9%. Across these years the share ran from 28.6% to 43.9%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 123 tests reported to CDC for Montgomery 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

Montgomery County, Compared

Montgomery County radon figures, compared

Calculated by Radon411

In Montgomery County, about 4 in 10 reported tests in 2017 (54 of 123) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 12.2 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Montgomery County runs 10.2 points above its state.

Of 6 neighbours with a figure, none reported a larger share at or above 4 pCi/L; the spread is 25.6% (Macoupin County) to 43.7% (Sangamon County). By share, Montgomery County is 34th of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 28.6% and 2017 closed at 43.9% (up 15.3 points), with 2017 the high at 43.9%. Half the tests came in under 3.3 pCi/L and half over it; the single highest reached 35.8 pCi/L. Below the action level, 36 tests (29.3%) came in under 2 pCi/L, against 37.7% statewide, and 33 tests (26.8%) fell between 2 and 4, against 28.6% statewide.

Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 43.9% share point the same way here. USGS geology rates 89% of the county's land moderate radon potential.

The busiest year on file was 2017, with 123 tests reported; the quietest, 2014, had 42.

Share of reported tests at or above 4 pCi/L by year, Montgomery County against Illinois2014 to 2017, years with 30 or more tests: Montgomery County 28.6% to 43.9%, the state's pooled share 33.7% in 2017.
Montgomery CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Montgomery County against Illinois: data table
YearTestsMontgomery County, at or above 4 pCi/LIllinois, pooled
20144228.6%37.8%
20156934.8%36.6%
201712343.9%33.7%
Montgomery County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Montgomery County
Montgomery County12343.9%3.3 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−10.2 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−12.2 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+25.3 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−35.5 points
Shelby County, ILborders it2171.4%5.2 pCi/L+27.5 points
Sangamon County, ILborders it3,37843.7%3.7 pCi/L−0.2 points
Christian County, ILborders it21342.3%3.5 pCi/L−1.6 points
Bond County, ILborders it7532.0%2.6 pCi/L−11.9 points
Madison County, ILborders it5,21429.5%2.6 pCi/L−14.4 points
Fayette County, ILborders it5726.3%2.5 pCi/L−17.6 points
Macoupin County, ILborders it25825.6%2.2 pCi/L−18.3 points
Where Montgomery County's reported results fell, 2017, beside Illinois and the United States
ResultMontgomery County testsMontgomery County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L3629.3%37.7%43.5%−8.4 points
2 to 4 pCi/L3326.8%28.6%24.8%−1.8 points
4 pCi/L and above5443.9%33.7%31.7%+10.2 points
Montgomery 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
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
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
Montgomery County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201712343.9%3.3 pCi/L35.8 pCi/L33.7%+9.1 points
20156934.8%2.6 pCi/L18.6 pCi/L36.6%+6.2 points
20144228.6%1.8 pCi/L6.0 pCi/L37.8%First on file

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

Montgomery County, Geology

The ground under Montgomery County

Predicted

Most of the ground under Montgomery County is one class on USGS's geologic map: 88.8% of its land is moderate radon potential, with 11.2% high. The map puts 88.8% of Montgomery County in the area it calls Southern Central Lowland Province and 11.2% in Galesburg Plain. USGS gives the first a radon index of 9, in the moderate band (9 to 11), and the second 13, in the high band (12 to 17).

USGS's geologic areas under Montgomery County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Southern Central Lowland ProvinceIllinoian glacial deposits, sandstone, and gray shale.Moderate988.8%
Galesburg PlainIllinoian glacial deposits and loess over Paleozoic sedimentary rocks.High1311.2%

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

Montgomery County beside the ground around it

Illinois as a whole has more high-potential ground than Montgomery County: 64.5% of its land, against 11.2% here. Of the 7 counties that border it, 4 have more high-potential ground, Sangamon County the most at 100%.

Share of land by USGS radon potential: Montgomery County, the 7 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Montgomery CountyZone 2None88.8%11.2%
Christian CountyZone 2None16.9%83.1%
Bond CountyZone 2None100%None
Macoupin CountyZone 2None42.4%57.6%
Fayette CountyZone 2None100%None
Sangamon CountyZone 1NoneNone100%
Shelby CountyZone 2None54.9%45.1%
Madison CountyZone 2None91.7%8.3%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

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

Local help

Montgomery County, Local resources

Radon testing and mitigation in Montgomery 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

Montgomery County, Questions

Questions about radon in Montgomery County

Are radon levels high in Montgomery County?

In 2017, 43.9% of the radon tests reported to CDC for Montgomery 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, 33 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Montgomery County?

Montgomery County borders 7 counties: Christian County, Bond County, Macoupin County, Fayette County, Sangamon County, Shelby County and Madison County.

Products

Montgomery County, Products

Testing a home in Montgomery County

In Montgomery County, 43.9% of 123 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Montgomery County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Montgomery County homes, compared

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Montgomery County, Bordering counties

Counties bordering Montgomery County

Calculated by Radon411

Montgomery County, Cities and towns

Cities and towns in Montgomery County

About 28,076 people live in Montgomery County by the Census Bureau's estimate for July 1, 2025, 168 fewer than in 2020 (−0.6%). That works out to 40 people per square mile of land. Its largest town, Litchfield, has 6,598 residents, 23.5% of the total. Reported testing is thin here: 123 tests over 2017, or 4.4 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.

From Litchfield to Wenonah, CDC publishes no figure by town: each reads Montgomery County's.

The 12 largest cities and towns in Montgomery County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Litchfield6,598−2.4%23.5%
Hillsboro6,184+5.3%22.0%
Nokomis2,133−2.2%7.6%
Raymond920−2.3%3.3%
Witt770−2.3%2.7%
Taylor Springs727−1.5%2.6%
Farmersville668−2.3%2.4%
Coffeen627−2.3%2.2%
Schram City555−1.9%2.0%
Irving365−2.4%1.3%
Panamaextends beyond Montgomery County325−1.8%Counted whole
Coalton302−2.3%1.1%
  • Fillmore
  • Waggoner
  • Harvel (part)
  • Butler
  • Donnellson (part)
  • Ohlman
  • Walshville
  • Wenonah

20 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 Montgomery County is counted whole, so it has no share.

Montgomery County, Homes

Homes in Montgomery County

Montgomery County is a place of houses on their own lots: 83% of its 12,528 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1963, close to Illinois' 1970: 47% date from before 1960 and 13% from 2000 or later. Owners live in 76% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Montgomery County, Illinois, 2019 to 2023
HomesMontgomery CountyIllinois
Housing units12,5285,443,501
Detached houses83%58%
In buildings of 5 or more5%22%
Mobile homes6%2%
Built before 196047%38%
Built since 200013%16%
Middle year built19631970
Owner-occupied76%67%

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