Is radon high in Illinois?

Illinois's population-weighted predicted basement average is 1.9 pCi/L, close to the US average of 1.8. 1 of its 102 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 82 are in the 2-4 "consider fixing" range and 19 are below 2. 0.4% of Illinois ZIP codes are predicted at 4 or higher.

Which Illinois county has the highest radon?

Knox County has the highest predicted basement average in Illinois at 4.0 pCi/L (EPA Zone 1). The lowest is Cook County at 1.2 pCi/L. These are area figures; individual homes in any county can test far higher.

How many EPA Zone 1 counties are in Illinois?

56 of Illinois's 102 counties (55%) are EPA Zone 1 (highest potential), 43 are Zone 2 and 3 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.

Should I test for radon in Illinois?

Yes. Even though Illinois's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 66.1% of Illinois ZIP codes are still predicted at 2 pCi/L or higher.

Radon levels in Illinois: Low

Name: Radon levels by county for Illinois
Creator: RadonGrade
License: https://creativecommons.org/licenses/by/4.0/

The model predicts a population-weighted basement average of 1.9 pCi/L (model estimate) across Illinois's 102 counties - close to the US average of 1.8 pCi/L. Above-ground floors average 1.2 pCi/L.

Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

56 / 102

EPA Zone 1 counties (55%)

43 / 3

Zone 2 / Zone 3 counties

counties predicted ≥ 4 pCi/L

0.4%

of ZIP codes predicted ≥ 4 pCi/L

Test Illinois once anyway - radon varies house to house

The predicted basement average here is 1.9 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.

Get a short-term test kit →Or track it with a continuous monitor

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What the data says about radon in Illinois

56 of Illinois's 102 counties are EPA Zone 1 (55%), 43 are Zone 2 and 3 are Zone 3 on the EPA's county-level map. Zone 1 - the highest-potential class, predicted screening average above 4 pCi/L - is the most common designation in Illinois. The zones were drawn once, from geology and the tests available in 1993, and the EPA itself notes that homes with elevated radon exist in all three zones.

Weighted by where people live, Illinois's predicted basement average is 1.9 pCi/L - close to the US average of 1.8 - which puts the state in the low range. Of the 102 counties with predictions, 1 are predicted at or above 4 pCi/L, 82 in the 2-4 band and 19 below 2. The highest predicted county is Knox County at 4.0 pCi/L; the lowest is Cook County at 1.2 - a 2.8 pCi/L spread that means a statewide average tells you little about any one county.

Nationally 4.2% of ZIPs are predicted at 4+ pCi/L and 48.7% at 2+; in Illinois it is 0.4% and 66.1% - below the US share at the action level but above it at 2 pCi/L. With more than half of ZIPs above 2, a test is worth doing before any purchase or renovation here.

Illinois counties by predicted radon

Sorted highest to lowest predicted basement average (model estimate). 102 counties.

County	Predicted basement	Upstairs	Grade	EPA zone	ZIPs
Knox County	4.0 pCi/L	2.4	High	EPA Zone 1	16
Warren County	4.0 pCi/L	2.1	Moderate	EPA Zone 1	8
Morgan County	3.6 pCi/L	1.9	Moderate	EPA Zone 1	8
Fulton County	3.6 pCi/L	2.0	Moderate	EPA Zone 1	15
Stark County	3.6 pCi/L	2.0	Moderate	EPA Zone 1	4
Stephenson County	3.5 pCi/L	1.8	Moderate	EPA Zone 1	12
Mercer County	3.5 pCi/L	2.1	Moderate	EPA Zone 1	12
Logan County	3.5 pCi/L	2.0	Moderate	EPA Zone 1	11
Henry County	3.4 pCi/L	2.1	Moderate	EPA Zone 1	14
Adams County	3.4 pCi/L	1.8	Moderate	EPA Zone 1	15
Schuyler County	3.3 pCi/L	2.0	Moderate	EPA Zone 1	6
Hancock County	3.3 pCi/L	1.9	Moderate	EPA Zone 1	15
Menard County	3.3 pCi/L	2.0	Moderate	EPA Zone 1	5
Marshall County	3.3 pCi/L	1.9	Moderate	EPA Zone 1	6
Jo Daviess County	3.3 pCi/L	2.1	Moderate	EPA Zone 1	8
De Witt County	3.2 pCi/L	2.0	Moderate	EPA Zone 1	7
Carroll County	3.2 pCi/L	2.0	Moderate	EPA Zone 1	7
Mason County	3.2 pCi/L	1.8	Moderate	EPA Zone 1	8
Pike County	3.2 pCi/L	1.8	Moderate	EPA Zone 1	15
Scott County	3.2 pCi/L	1.9	Moderate	EPA Zone 1	2
Cass County	3.2 pCi/L	1.8	Moderate	EPA Zone 1	5
Edgar County	3.2 pCi/L	1.9	Moderate	EPA Zone 1	6
Woodford County	3.2 pCi/L	2.0	Moderate	EPA Zone 1	12
Greene County	3.2 pCi/L	1.8	Moderate	EPA Zone 1	8
Putnam County	3.2 pCi/L	1.8	Moderate	EPA Zone 1	5
Moultrie County	3.2 pCi/L	2.0	Moderate	EPA Zone 1	5
Tazewell County	3.1 pCi/L	1.9	Moderate	EPA Zone 1	16
Brown County	3.1 pCi/L	1.8	Moderate	EPA Zone 1	3
Bureau County	3.1 pCi/L	2.2	Moderate	EPA Zone 1	16
Douglas County	3.1 pCi/L	1.9	Moderate	EPA Zone 1	6
Henderson County	3.1 pCi/L	1.6	Moderate	EPA Zone 1	8
Jersey County	3.1 pCi/L	1.8	Moderate	EPA Zone 1	8
McDonough County	3.1 pCi/L	2.2	Moderate	EPA Zone 1	10
Ford County	3.0 pCi/L	1.8	Moderate	EPA Zone 1	8
Christian County	3.0 pCi/L	1.6	Moderate	EPA Zone 2	13
Ogle County	3.0 pCi/L	1.9	Moderate	EPA Zone 1	14
Piatt County	3.0 pCi/L	1.9	Moderate	EPA Zone 1	10
Livingston County	3.0 pCi/L	1.8	Moderate	EPA Zone 1	16
Calhoun County	3.0 pCi/L	1.5	Moderate	EPA Zone 1	6
Lee County	3.0 pCi/L	1.9	Moderate	EPA Zone 1	11
Whiteside County	3.0 pCi/L	1.8	Moderate	EPA Zone 1	11
LaSalle County	2.9 pCi/L	1.8	Moderate	EPA Zone 1	21
Coles County	2.9 pCi/L	1.9	Moderate	EPA Zone 1	6
Peoria County	2.9 pCi/L	1.7	Moderate	EPA Zone 1	21
Sangamon County	2.9 pCi/L	1.7	Moderate	EPA Zone 1	24
Champaign County	2.8 pCi/L	1.9	Moderate	EPA Zone 1	27
Rock Island County	2.8 pCi/L	1.5	Moderate	EPA Zone 1	14
McLean County	2.8 pCi/L	1.7	Moderate	EPA Zone 1	24
Monroe County	2.7 pCi/L	1.3	Moderate	EPA Zone 2	6
Vermilion County	2.7 pCi/L	1.7	Moderate	EPA Zone 1	21
Boone County	2.7 pCi/L	1.8	Moderate	EPA Zone 1	5
Grundy County	2.7 pCi/L	1.7	Moderate	EPA Zone 1	7
Kendall County	2.6 pCi/L	1.7	Moderate	EPA Zone 1	7
Macon County	2.6 pCi/L	1.6	Moderate	EPA Zone 1	13
Macoupin County	2.6 pCi/L	1.5	Moderate	EPA Zone 2	15
Shelby County	2.6 pCi/L	1.5	Moderate	EPA Zone 2	12
Iroquois County	2.5 pCi/L	1.5	Moderate	EPA Zone 1	17
Kankakee County	2.5 pCi/L	1.6	Moderate	EPA Zone 2	14
DeKalb County	2.4 pCi/L	1.9	Moderate	EPA Zone 1	13
Winnebago County	2.3 pCi/L	1.5	Moderate	EPA Zone 1	17
Clinton County	2.3 pCi/L	1.2	Moderate	EPA Zone 2	8
Washington County	2.3 pCi/L	1.2	Moderate	EPA Zone 2	8
Randolph County	2.2 pCi/L	1.1	Moderate	EPA Zone 2	10
St. Clair County	2.2 pCi/L	1.1	Moderate	EPA Zone 2	25
Union County	2.2 pCi/L	1.4	Moderate	EPA Zone 2	6
Kane County	2.2 pCi/L	1.6	Moderate	EPA Zone 1	18
Hamilton County	2.2 pCi/L	1.1	Moderate	EPA Zone 2	3
Madison County	2.2 pCi/L	1.3	Moderate	EPA Zone 2	25
Bond County	2.2 pCi/L	1.1	Moderate	EPA Zone 2	7
Will County	2.1 pCi/L	1.4	Moderate	EPA Zone 2	30
Perry County	2.1 pCi/L	1.1	Moderate	EPA Zone 2	5
Clark County	2.1 pCi/L	1.1	Moderate	EPA Zone 2	7
McHenry County	2.1 pCi/L	1.6	Moderate	EPA Zone 2	18
Montgomery County	2.1 pCi/L	1.2	Moderate	EPA Zone 2	13
Jackson County	2.1 pCi/L	1.1	Moderate	EPA Zone 2	14
Johnson County	2.1 pCi/L	1.3	Moderate	EPA Zone 2	7
Fayette County	2.0 pCi/L	1.1	Moderate	EPA Zone 2	9
Marion County	2.0 pCi/L	0.9	Moderate	EPA Zone 2	10
Effingham County	2.0 pCi/L	1.0	Moderate	EPA Zone 2	7
Jefferson County	2.0 pCi/L	1.0	Moderate	EPA Zone 2	12
Wabash County	2.0 pCi/L	1.1	Moderate	EPA Zone 2	2
Cumberland County	2.0 pCi/L	1.1	Moderate	EPA Zone 2	5
Pope County	2.0 pCi/L	1.2	Moderate	EPA Zone 2	5
Franklin County	2.0 pCi/L	1.0	Low	EPA Zone 2	12
Clay County	1.9 pCi/L	1.0	Low	EPA Zone 2	6
Williamson County	1.9 pCi/L	1.0	Low	EPA Zone 2	8
Richland County	1.9 pCi/L	1.0	Low	EPA Zone 2	6
Hardin County	1.9 pCi/L	1.2	Low	EPA Zone 2	3
Jasper County	1.9 pCi/L	1.0	Low	EPA Zone 2	7
White County	1.9 pCi/L	1.0	Low	EPA Zone 2	9
Crawford County	1.9 pCi/L	1.0	Low	EPA Zone 2	6
Edwards County	1.9 pCi/L	1.0	Low	EPA Zone 2	4
Lawrence County	1.9 pCi/L	1.0	Low	EPA Zone 2	4
Gallatin County	1.9 pCi/L	1.1	Low	EPA Zone 2	5
Saline County	1.9 pCi/L	1.0	Low	EPA Zone 2	5
DuPage County	1.8 pCi/L	1.2	Low	EPA Zone 2	36
Alexander County	1.7 pCi/L	0.9	Low	EPA Zone 3	5
Wayne County	1.7 pCi/L	0.9	Low	EPA Zone 2	12
Lake County	1.7 pCi/L	1.2	Low	EPA Zone 2	26
Massac County	1.7 pCi/L	0.9	Low	EPA Zone 3	4
Pulaski County	1.6 pCi/L	0.9	Low	EPA Zone 3	7
Cook County	1.2 pCi/L	0.8	Low	EPA Zone 2	161

Radon levels in Illinois cities

The 34 most-populous Illinois places among the 1,000 largest US cities (Census incorporated places and CDPs), by population. City figures are ZIP-land-weighted means of the model's ZIP predictions (model estimate).

City	Population	Predicted basement	Upstairs	Grade	ZIPs ≥ 4
Chicago	2,664,452	1.0 pCi/L	0.7	Low	0%
Aurora	177,563	2.1 pCi/L	1.5	Moderate	0%
Joliet	150,489	2.4 pCi/L	1.5	Moderate	0%
Naperville	150,245	1.8 pCi/L	1.3	Low	0%
Rockford	146,120	2.3 pCi/L	1.5	Moderate	0%
Elgin	113,310	2.2 pCi/L	1.6	Moderate	0%
Springfield	112,544	2.8 pCi/L	1.7	Moderate	0%
Peoria	110,460	2.7 pCi/L	1.6	Moderate	0%
Champaign	89,189	2.6 pCi/L	1.7	Moderate	0%
Waukegan	87,642	1.4 pCi/L	1.0	Low	0%
Cicero	81,004	1.1 pCi/L	0.7	Low	0%
Bloomington	78,587	2.5 pCi/L	1.6	Moderate	0%
Schaumburg	75,750	1.5 pCi/L	1.0	Low	0%
Evanston	75,070	0.9 pCi/L	0.7	Low	0%
Arlington Heights	74,495	1.6 pCi/L	1.1	Low	0%
Bolingbrook	74,088	2.0 pCi/L	1.4	Low	0%
Decatur	68,670	2.6 pCi/L	1.6	Moderate	0%
Skokie	64,937	1.2 pCi/L	0.9	Low	0%
Palatine	64,869	2.0 pCi/L	1.3	Moderate	0%
Des Plaines	58,010	1.3 pCi/L	1.0	Low	0%
Orland Park	57,074	1.8 pCi/L	1.2	Low	0%
Oak Lawn	55,734	1.3 pCi/L	1.1	Low	0%
Berwyn	54,414	1.3 pCi/L	0.8	Low	0%
Mount Prospect	54,298	1.5 pCi/L	1.1	Low	0%
Tinley Park	53,886	1.5 pCi/L	1.2	Low	0%
Wheaton	52,938	1.5 pCi/L	1.1	Low	0%
Normal	52,618	2.8 pCi/L	1.8	Moderate	0%
Oak Park	52,055	1.1 pCi/L	0.9	Low	0%
Hoffman Estates	50,179	1.8 pCi/L	1.4	Low	0%
Downers Grove	49,706	1.8 pCi/L	1.1	Low	0%
Plainfield	47,448	2.3 pCi/L	1.6	Moderate	0%
Glenview	46,904	1.6 pCi/L	1.1	Low	0%
Elmhurst	45,336	1.6 pCi/L	1.3	Low	0%
Lombard	43,779	1.8 pCi/L	1.1	Low	0%

Highest-radon ZIP codes in Illinois

The 10 Illinois ZIP codes with the highest predicted basement average (model estimate), out of 1,255 modeled. A ZIP average is still an area figure - neighboring homes routinely test several pCi/L apart.

ZIP	County	Predicted basement	Upstairs	Grade
61523	Peoria County	4.3 pCi/L	2.0	High
61401	Knox County	4.3 pCi/L	2.5	High
61462	Warren County	4.2 pCi/L	2.2	High
61238	Henry County	4.1 pCi/L	2.4	High
61443	Henry County	4.0 pCi/L	2.2	High
61520	Fulton County	3.9 pCi/L	2.1	Moderate
62305	Adams County	3.9 pCi/L	2.0	Moderate
61529	Peoria County	3.8 pCi/L	2.2	Moderate
61231	Mercer County	3.8 pCi/L	2.3	Moderate
61273	Henry County	3.8 pCi/L	2.2	Moderate

Illinois radon questions

Is radon high in Illinois?: Illinois's population-weighted predicted basement average is 1.9 pCi/L, close to the US average of 1.8. 1 of its 102 modeled counties are predicted at or above the EPA action level of 4 pCi/L, 82 are in the 2-4 "consider fixing" range and 19 are below 2. 0.4% of Illinois ZIP codes are predicted at 4 or higher.
Which Illinois county has the highest radon?: Knox County has the highest predicted basement average in Illinois at 4.0 pCi/L (EPA Zone 1). The lowest is Cook County at 1.2 pCi/L. These are area figures; individual homes in any county can test far higher.
How many EPA Zone 1 counties are in Illinois?: 56 of Illinois's 102 counties (55%) are EPA Zone 1 (highest potential), 43 are Zone 2 and 3 are Zone 3. The EPA zone map dates from 1993; the predicted values on this page come from a 2001-2021 model built on millions of actual tests, so the two can disagree for a given county.
Should I test for radon in Illinois?: Yes. Even though Illinois's predicted average is below 2 pCi/L, the EPA recommends every home be tested - radon varies house to house, and 66.1% of Illinois ZIP codes are still predicted at 2 pCi/L or higher.

Illinois radon program

Illinois's radon program page is at iemaohs.illinois.gov and, when we checked it, offered low-cost test kits. The EPA also keeps a directory of every state radon contact: EPA state radon contacts page. Then read how to test and what mitigation costs.