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Counties with the Highest Radon Potential in Illinois

The top 25 of 102 Illinois counties on GIS Map, ranked by EPA radon zone, where zone 1 carries the highest predicted indoor radon potential and zone 3 the lowest.

#CountyEPA radon zone
1Alexander County
3
2Massac County
3
3Pulaski County
3
4Bond County
2
5Christian County
2
6Clark County
2
7Clay County
2
8Clinton County
2
9Cook County
2
10Crawford County
2
11Cumberland County
2
12DuPage County
2
13Edwards County
2
14Effingham County
2
15Fayette County
2
16Franklin County
2
17Gallatin County
2
18Hamilton County
2
19Hardin County
2
20Jackson County
2
21Jasper County
2
22Jefferson County
2
23Johnson County
2
24Kankakee County
2
25Lake County
2

Source: EPA Map of Radon Zones (September 2025). All counties with data are ranked. Estimates carry margins of error.

Citing this page: GIS Map, “Counties with the Highest Radon Potential in Illinois”, https://gismap.land/rankings/illinois/highest-radon-counties. Figures from EPA Map of Radon Zones (September 2025).

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