Illinois Radon Levels
56Zone 1 (High)
43Zone 2 (Moderate)
3Zone 3 (Low)
55% of counties in Illinois are classified as EPA Zone 1 (highest radon potential), meaning predicted average indoor radon levels exceed 4 pCi/L — the EPA action level. The EPA recommends that all homes be tested for radon, regardless of zone classification.
| County | EPA Zone | Risk Level |
|---|---|---|
| Adams County | Zone 1 | Highest Potential |
| Alexander County | Zone 3 | Lowest Potential |
| Bond County | Zone 2 | Moderate Potential |
| Boone County | Zone 1 | Highest Potential |
| Brown County | Zone 1 | Highest Potential |
| Bureau County | Zone 1 | Highest Potential |
| Calhoun County | Zone 1 | Highest Potential |
| Carroll County | Zone 1 | Highest Potential |
| Cass County | Zone 1 | Highest Potential |
| Champaign County | Zone 1 | Highest Potential |
| Christian County | Zone 2 | Moderate Potential |
| Clark County | Zone 2 | Moderate Potential |
| Clay County | Zone 2 | Moderate Potential |
| Clinton County | Zone 2 | Moderate Potential |
| Coles County | Zone 1 | Highest Potential |
| Cook County | Zone 2 | Moderate Potential |
| Crawford County | Zone 2 | Moderate Potential |
| Cumberland County | Zone 2 | Moderate Potential |
| DeKalb County | Zone 1 | Highest Potential |
| De Witt County | Zone 1 | Highest Potential |
| Douglas County | Zone 1 | Highest Potential |
| DuPage County | Zone 2 | Moderate Potential |
| Edgar County | Zone 1 | Highest Potential |
| Edwards County | Zone 2 | Moderate Potential |
| Effingham County | Zone 2 | Moderate Potential |
| Fayette County | Zone 2 | Moderate Potential |
| Ford County | Zone 1 | Highest Potential |
| Franklin County | Zone 2 | Moderate Potential |
| Fulton County | Zone 1 | Highest Potential |
| Gallatin County | Zone 2 | Moderate Potential |
| Greene County | Zone 1 | Highest Potential |
| Grundy County | Zone 1 | Highest Potential |
| Hamilton County | Zone 2 | Moderate Potential |
| Hancock County | Zone 1 | Highest Potential |
| Hardin County | Zone 2 | Moderate Potential |
| Henderson County | Zone 1 | Highest Potential |
| Henry County | Zone 1 | Highest Potential |
| Iroquois County | Zone 1 | Highest Potential |
| Jackson County | Zone 2 | Moderate Potential |
| Jasper County | Zone 2 | Moderate Potential |
| Jefferson County | Zone 2 | Moderate Potential |
| Jersey County | Zone 1 | Highest Potential |
| Jo Daviess County | Zone 1 | Highest Potential |
| Johnson County | Zone 2 | Moderate Potential |
| Kane County | Zone 1 | Highest Potential |
| Kankakee County | Zone 2 | Moderate Potential |
| Kendall County | Zone 1 | Highest Potential |
| Knox County | Zone 1 | Highest Potential |
| Lake County | Zone 2 | Moderate Potential |
| LaSalle County | Zone 1 | Highest Potential |
| Lawrence County | Zone 2 | Moderate Potential |
| Lee County | Zone 1 | Highest Potential |
| Livingston County | Zone 1 | Highest Potential |
| Logan County | Zone 1 | Highest Potential |
| McDonough County | Zone 1 | Highest Potential |
| McHenry County | Zone 2 | Moderate Potential |
| McLean County | Zone 1 | Highest Potential |
| Macon County | Zone 1 | Highest Potential |
| Macoupin County | Zone 2 | Moderate Potential |
| Madison County | Zone 2 | Moderate Potential |
| Marion County | Zone 2 | Moderate Potential |
| Marshall County | Zone 1 | Highest Potential |
| Mason County | Zone 1 | Highest Potential |
| Massac County | Zone 3 | Lowest Potential |
| Menard County | Zone 1 | Highest Potential |
| Mercer County | Zone 1 | Highest Potential |
| Monroe County | Zone 2 | Moderate Potential |
| Montgomery County | Zone 2 | Moderate Potential |
| Morgan County | Zone 1 | Highest Potential |
| Moultrie County | Zone 1 | Highest Potential |
| Ogle County | Zone 1 | Highest Potential |
| Peoria County | Zone 1 | Highest Potential |
| Perry County | Zone 2 | Moderate Potential |
| Piatt County | Zone 1 | Highest Potential |
| Pike County | Zone 1 | Highest Potential |
| Pope County | Zone 2 | Moderate Potential |
| Pulaski County | Zone 3 | Lowest Potential |
| Putnam County | Zone 1 | Highest Potential |
| Randolph County | Zone 2 | Moderate Potential |
| Richland County | Zone 2 | Moderate Potential |
| Rock Island County | Zone 1 | Highest Potential |
| St. Clair County | Zone 2 | Moderate Potential |
| Saline County | Zone 2 | Moderate Potential |
| Sangamon County | Zone 1 | Highest Potential |
| Schuyler County | Zone 1 | Highest Potential |
| Scott County | Zone 1 | Highest Potential |
| Shelby County | Zone 2 | Moderate Potential |
| Stark County | Zone 1 | Highest Potential |
| Stephenson County | Zone 1 | Highest Potential |
| Tazewell County | Zone 1 | Highest Potential |
| Union County | Zone 2 | Moderate Potential |
| Vermilion County | Zone 1 | Highest Potential |
| Wabash County | Zone 2 | Moderate Potential |
| Warren County | Zone 1 | Highest Potential |
| Washington County | Zone 2 | Moderate Potential |
| Wayne County | Zone 2 | Moderate Potential |
| White County | Zone 2 | Moderate Potential |
| Whiteside County | Zone 1 | Highest Potential |
| Will County | Zone 2 | Moderate Potential |
| Williamson County | Zone 2 | Moderate Potential |
| Winnebago County | Zone 1 | Highest Potential |
| Woodford County | Zone 1 | Highest Potential |