Radon and home risks by county
Radon in Illinois
56 of Illinois's 102 counties are in EPA's highest radon zone, home to about 27% of the state's residents. Radon zones describe an area's potential; EPA recommends testing every home regardless of zone.
Zone 1 counties
56
high radon potential
Zone 2 counties
43
moderate potential
Zone 3 counties
3
low potential
Counties with water violations
91
since 2016; 43 with unresolved ones
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Zone 1: high potential (56 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Adams County | 64,109 | 19 | 6 | 1 |
| Boone County | 53,313 | 11 | 0 | 0 |
| Brown County | 6,307 | 5 | 0 | 0 |
| Bureau County | 32,486 | 24 | 15 | 4 |
| Calhoun County | 4,224 | 5 | 1 | 0 |
| Carroll County | 15,444 | 9 | 25 | 1 |
| Cass County | 12,713 | 7 | 0 | 0 |
| Champaign County | 212,374 | 38 | 26 | 0 |
| Coles County | 46,423 | 10 | 1 | 0 |
| De Witt County | 15,319 | 8 | 3 | 0 |
| DeKalb County | 101,335 | 20 | 8 | 1 |
| Douglas County | 19,824 | 11 | 7 | 0 |
| Edgar County | 16,398 | 7 | 24 | 1 |
| Ford County | 13,451 | 11 | 5 | 0 |
| Fulton County | 32,510 | 18 | 30 | 0 |
| Greene County | 11,417 | 10 | 20 | 0 |
| Grundy County | 53,835 | 20 | 11 | 0 |
| Hancock County | 17,008 | 11 | 10 | 0 |
| Henderson County | 6,048 | 7 | 1 | 0 |
| Henry County | 48,177 | 41 | 44 | 2 |
| Iroquois County | 26,067 | 26 | 16 | 2 |
| Jersey County | 21,150 | 4 | 0 | 0 |
| Jo Daviess County | 21,528 | 14 | 3 | 0 |
| Kane County | 520,997 | 39 | 9 | 0 |
| Kendall County | 143,171 | 9 | 12 | 0 |
| Knox County | 48,716 | 17 | 5 | 1 |
| LaSalle County | 108,390 | 37 | 63 | 3 |
| Lee County | 33,544 | 17 | 19 | 0 |
| Livingston County | 35,375 | 16 | 6 | 1 |
| Logan County | 27,518 | 14 | 16 | 0 |
| Macon County | 100,737 | 15 | 13 | 2 |
| Marshall County | 11,552 | 11 | 3 | 1 |
| Mason County | 12,543 | 6 | 2 | 0 |
| McDonough County | 26,662 | 14 | 12 | 0 |
| McLean County | 172,069 | 36 | 33 | 1 |
| Menard County | 11,963 | 7 | 0 | 0 |
| Mercer County | 15,292 | 14 | 3 | 0 |
| Morgan County | 32,618 | 13 | 9 | 1 |
| Moultrie County | 14,365 | 6 | 0 | 0 |
| Ogle County | 51,345 | 24 | 11 | 0 |
| Peoria County | 179,630 | 21 | 4 | 0 |
| Piatt County | 16,628 | 9 | 7 | 0 |
| Pike County | 14,258 | 13 | 1 | 1 |
| Putnam County | 5,633 | 8 | 4 | 0 |
| Rock Island County | 142,731 | 49 | 18 | 4 |
| Sangamon County | 194,345 | 42 | 6 | 0 |
| Schuyler County | 6,750 | 5 | 2 | 0 |
| Scott County | 4,880 | 6 | 6 | 0 |
| Stark County | 5,272 | 4 | 2 | 2 |
| Stephenson County | 43,088 | 13 | 7 | 1 |
| Tazewell County | 129,821 | 30 | 17 | 1 |
| Vermilion County | 71,106 | 20 | 8 | 3 |
| Warren County | 16,217 | 6 | 2 | 0 |
| Whiteside County | 54,657 | 12 | 8 | 1 |
| Winnebago County | 283,790 | 28 | 13 | 0 |
| Woodford County | 38,290 | 19 | 16 | 3 |
Zone 2: moderate potential (43 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Bond County | 16,576 | 9 | 38 | 3 |
| Christian County | 33,247 | 14 | 14 | 1 |
| Clark County | 15,076 | 6 | 6 | 1 |
| Clay County | 12,821 | 6 | 2 | 1 |
| Clinton County | 37,087 | 20 | 5 | 2 |
| Cook County | 5,182,617 | 163 | 21 | 5 |
| Crawford County | 18,388 | 7 | 1 | 1 |
| Cumberland County | 10,305 | 4 | 4 | 0 |
| DuPage County | 937,142 | 48 | 3 | 0 |
| Edwards County | 5,984 | 4 | 0 | 0 |
| Effingham County | 34,602 | 12 | 11 | 0 |
| Fayette County | 21,157 | 9 | 14 | 0 |
| Franklin County | 37,033 | 22 | 2 | 0 |
| Gallatin County | 4,690 | 7 | 1 | 0 |
| Hamilton County | 7,818 | 4 | 1 | 1 |
| Hardin County | 3,550 | 5 | 0 | 0 |
| Jackson County | 53,199 | 20 | 17 | 0 |
| Jasper County | 9,092 | 4 | 0 | 0 |
| Jefferson County | 36,107 | 13 | 0 | 0 |
| Johnson County | 13,320 | 6 | 3 | 0 |
| Kankakee County | 106,410 | 21 | 10 | 0 |
| Lake County | 718,604 | 103 | 9 | 1 |
| Lawrence County | 14,801 | 8 | 2 | 2 |
| Macoupin County | 43,895 | 30 | 55 | 2 |
| Madison County | 263,017 | 41 | 15 | 2 |
| Marion County | 36,437 | 15 | 1 | 0 |
| McHenry County | 315,959 | 32 | 5 | 0 |
| Monroe County | 34,969 | 6 | 8 | 0 |
| Montgomery County | 27,615 | 18 | 22 | 1 |
| Perry County | 20,272 | 7 | 19 | 1 |
| Pope County | 3,703 | 2 | 12 | 0 |
| Randolph County | 29,903 | 14 | 22 | 1 |
| Richland County | 15,362 | 7 | 2 | 0 |
| Saline County | 22,826 | 11 | 3 | 2 |
| Shelby County | 20,542 | 9 | 3 | 1 |
| St. Clair County | 251,149 | 28 | 5 | 1 |
| Union County | 16,886 | 9 | 15 | 0 |
| Wabash County | 10,979 | 5 | 1 | 0 |
| Washington County | 13,535 | 12 | 2 | 0 |
| Wayne County | 15,928 | 10 | 8 | 0 |
| White County | 13,395 | 9 | 1 | 1 |
| Will County | 708,583 | 52 | 8 | 2 |
| Williamson County | 67,064 | 24 | 18 | 2 |
Zone 3: low potential (3 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Alexander County | 4,594 | 6 | 0 | 0 |
| Massac County | 13,627 | 4 | 2 | 0 |
| Pulaski County | 4,879 | 6 | 1 | 0 |
How to read this table
Water systems counts community systems that list the county in their service area; one system can serve several counties. Health violations are breaches of a legal limit or treatment rule recorded by EPA since January 2016, not paperwork lapses. A violation stays unresolved until the state records it as fixed.
Other states
- Arizona
- California
- Colorado
- Florida
- Idaho
- Iowa
- Michigan
- Minnesota
- New Jersey
- New York
- Ohio
- Pennsylvania
- Texas
- Utah
Sources: EPA Map of Radon Zones, EPA ECHO Safe Drinking Water Act data (2026Q3, published October 2026), US Census Bureau Vintage 2024 estimates. See the methodology.