Radon in Illinois: radon map by county
EPA's Map of Radon Zones puts 56 of Illinois's 102 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 43 in Zone 2 and 3 in Zone 3. Of 85,532 building tests that radon laboratories reported for 2008 to 2017, 43.2% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 9 of 42 states with 1,000+ tests). The highest county share is Stark County (80.5% of 74 tests).
Radon by county in Illinois
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Adams County | Zone 1 | 3,064 | 4.5 | 55.2% |
| Alexander County | Zone 3 | 8 | 2.4 | 22.2% |
| Bond County | Zone 2 | 73 | 3.3 | 44.2% |
| Boone County | Zone 1 | 238 | 3.6 | 48.1% |
| Brown County | Zone 1 | 27 | 2.9 | 37.8% |
| Bureau County | Zone 1 | 213 | 4.6 | 57.5% |
| Calhoun County | Zone 1 | 7 | 4.5 | 66.7% |
| Carroll County | Zone 1 | 337 | 5.1 | 60.8% |
| Cass County | Zone 1 | 33 | 3.0 | 38.5% |
| Champaign County | Zone 1 | 6,807 | 4.0 | 50.2% |
| Christian County | Zone 2 | 163 | 3.7 | 46.3% |
| Clark County | Zone 2 | 60 | 2.0 | 22.1% |
| Clay County | Zone 2 | 59 | 1.1 | 14.7% |
| Clinton County | Zone 2 | 200 | 2.8 | 36.4% |
| Coles County | Zone 1 | 211 | 3.1 | 38.6% |
| Cook County | Zone 2 | 10,990 | 1.8 | 20.2% |
| Crawford County | Zone 2 | 139 | 1.8 | 19.3% |
| Cumberland County | Zone 2 | 43 | 1.8 | 21.8% |
| De Witt County | Zone 1 | 109 | 4.8 | 60.6% |
| DeKalb County | Zone 1 | 1,576 | 3.6 | 46.2% |
| Douglas County | Zone 1 | 177 | 3.4 | 42.7% |
| DuPage County | Zone 2 | 4,707 | 2.9 | 37.5% |
| Edgar County | Zone 1 | 87 | 3.2 | 37.9% |
| Edwards County | Zone 2 | 14 | 2.1 | 21.1% |
| Effingham County | Zone 2 | 585 | 3.0 | 37.9% |
| Fayette County | Zone 2 | 93 | 2.7 | 33.1% |
| Ford County | Zone 1 | 187 | 3.4 | 42.2% |
| Franklin County | Zone 2 | 151 | 1.8 | 19.6% |
| Fulton County | Zone 1 | 255 | 5.4 | 64.4% |
| Gallatin County | Zone 2 | 4 | 2.0 | 33.3% |
| Greene County | Zone 1 | 16 | 3.5 | 42.9% |
| Grundy County | Zone 1 | 257 | 3.1 | 40.9% |
| Hamilton County | Zone 2 | 24 | 1.9 | 23.3% |
| Hancock County | Zone 1 | 141 | 3.5 | 43.5% |
| Hardin County | Zone 2 | 2 | 1.4 | 22.2% |
| Henderson County | Zone 1 | 32 | 5.7 | 68.4% |
| Henry County | Zone 1 | 1,177 | 4.9 | 60.4% |
| Iroquois County | Zone 1 | 303 | 2.1 | 28% |
| Jackson County | Zone 2 | 361 | 2.3 | 28.5% |
| Jasper County | Zone 2 | 53 | 1.9 | 23.7% |
| Jefferson County | Zone 2 | 250 | 1.9 | 22.2% |
| Jersey County | Zone 1 | 68 | 3.2 | 38.9% |
| Jo Daviess County | Zone 1 | 714 | 4.6 | 57.2% |
| Johnson County | Zone 2 | 41 | 1.8 | 14.6% |
| Kane County | Zone 1 | 3,196 | 3.4 | 43.9% |
| Kankakee County | Zone 2 | 300 | 3.3 | 42.5% |
| Kendall County | Zone 1 | 819 | 3.6 | 46.9% |
| Knox County | Zone 1 | 689 | 6.1 | 65.9% |
| Lake County | Zone 2 | 5,174 | 2.5 | 30.2% |
| LaSalle County | Zone 1 | 636 | 4.1 | 51.6% |
| Lawrence County | Zone 2 | 31 | 1.8 | 18.8% |
| Lee County | Zone 1 | 161 | 3.3 | 41.9% |
| Livingston County | Zone 1 | 158 | 5.7 | 61.4% |
| Logan County | Zone 1 | 267 | 5.3 | 62.1% |
| Macon County | Zone 1 | 540 | 3.4 | 44.5% |
| Macoupin County | Zone 2 | 149 | 2.7 | 34.8% |
| Madison County | Zone 2 | 2,876 | 3.0 | 37.4% |
| Marion County | Zone 2 | 250 | 1.7 | 20.6% |
| Marshall County | Zone 1 | 173 | 6.0 | 63.9% |
| Mason County | Zone 1 | 78 | 3.5 | 43.1% |
| Massac County | Zone 3 | 28 | 1.9 | 15.2% |
| McDonough County | Zone 1 | 466 | 4.5 | 54.4% |
| McHenry County | Zone 2 | 2,209 | 3.2 | 42.4% |
| McLean County | Zone 1 | 3,398 | 4.3 | 52.8% |
| Menard County | Zone 1 | 82 | 4.2 | 51.3% |
| Mercer County | Zone 1 | 298 | 6.8 | 67.1% |
| Monroe County | Zone 2 | 710 | 3.5 | 44.2% |
| Montgomery County | Zone 2 | 170 | 2.8 | 36.9% |
| Morgan County | Zone 1 | 116 | 5.8 | 64.5% |
| Moultrie County | Zone 1 | 51 | 3.8 | 47.8% |
| Ogle County | Zone 1 | 701 | 5.5 | 62.5% |
| Peoria County | Zone 1 | 5,791 | 4.0 | 50.4% |
| Perry County | Zone 2 | 142 | 2.4 | 27.7% |
| Piatt County | Zone 1 | 475 | 4.0 | 51.7% |
| Pike County | Zone 1 | 80 | 3.8 | 46.3% |
| Pope County | Zone 2 | 7 | 1.8 | 0% |
| Pulaski County | Zone 3 | 9 | 2.0 | 18.2% |
| Putnam County | Zone 1 | 41 | 5.4 | 60.7% |
| Randolph County | Zone 2 | 108 | 3.2 | 40.3% |
| Richland County | Zone 2 | 99 | 1.8 | 18.9% |
| Rock Island County | Zone 1 | 3,067 | 3.8 | 48.3% |
| Saline County | Zone 2 | 71 | 1.7 | 20.7% |
| Sangamon County | Zone 1 | 1,929 | 4.2 | 52.2% |
| Schuyler County | Zone 1 | 29 | 3.8 | 43.9% |
| Scott County | Zone 1 | 9 | 4.4 | 50% |
| Shelby County | Zone 2 | 70 | 4.4 | 56.6% |
| St. Clair County | Zone 2 | 2,360 | 3.5 | 44.2% |
| Stark County | Zone 1 | 74 | 7.4 | 80.5% |
| Stephenson County | Zone 1 | 769 | 5.3 | 63.2% |
| Tazewell County | Zone 1 | 4,055 | 5.1 | 59.6% |
| Union County | Zone 2 | 64 | 1.9 | 25.3% |
| Vermilion County | Zone 1 | 279 | 3.8 | 48.8% |
| Wabash County | Zone 2 | 25 | 3.0 | 32.4% |
| Warren County | Zone 1 | 241 | 7.1 | 75.3% |
| Washington County | Zone 2 | 102 | 2.6 | 26.5% |
| Wayne County | Zone 2 | 62 | 1.4 | 15.1% |
| White County | Zone 2 | 25 | 2.9 | 29.4% |
| Whiteside County | Zone 1 | 507 | 3.7 | 47% |
| Will County | Zone 2 | 4,387 | 3.4 | 43.4% |
| Williamson County | Zone 2 | 450 | 1.3 | 13.3% |
| Winnebago County | Zone 1 | 1,211 | 3.4 | 44.2% |
| Woodford County | Zone 1 | 1,212 | 5.2 | 61.5% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
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Radon in Illinois: questions
What radon zone is Illinois?
EPA's 1993 map does not give states one zone; it zones each county. In Illinois, 56 counties are Zone 1, 43 Zone 2 and 3 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Illinois counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Stark County 80.5% (median 7.4 pCi/L, 74 tests); Warren County 75.3% (median 7.1 pCi/L, 241 tests); Henderson County 68.4% (median 5.7 pCi/L, 32 tests); Mercer County 67.1% (median 6.8 pCi/L, 298 tests); Knox County 65.9% (median 6.1 pCi/L, 689 tests).
How common is high radon in Illinois?
43.2% of the 85,532 tests in the laboratory data for Illinois (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Should I test for radon in Illinois?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Illinois
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Illinois · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.