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 modeled area averages; 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

The model predicts a population-weighted basement average of 1.9 pCi/L 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

Illinois counties by predicted radon

Sorted highest to lowest predicted basement average. 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

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 modeled area averages; 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

Many states offer free or discounted test kits and keep lists of certified mitigators. Find the Illinois radon office through the EPA state radon contacts page. Then read how to test and what mitigation costs.