Radon and home risks by county
Radon in Ohio
53 of Ohio's 88 counties are in EPA's highest radon zone, home to about 63% of the state's residents. Radon zones describe an area's potential; EPA recommends testing every home regardless of zone.
Zone 1 counties
53
high radon potential
Zone 2 counties
35
moderate potential
Zone 3 counties
0
low potential
Counties with water violations
77
since 2016; 20 with unresolved ones
Find your county by ZIP
Zone 1: high potential (53 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Adams County | 27,671 | 6 | 1 | 0 |
| Allen County | 100,866 | 8 | 5 | 0 |
| Ashland County | 52,420 | 10 | 2 | 0 |
| Auglaize County | 45,922 | 8 | 1 | 0 |
| Belmont County | 64,692 | 14 | 7 | 0 |
| Butler County | 399,542 | 12 | 0 | 0 |
| Carroll County | 26,460 | 6 | 4 | 3 |
| Champaign County | 38,907 | 12 | 1 | 0 |
| Clark County | 134,985 | 27 | 11 | 0 |
| Clinton County | 42,019 | 5 | 1 | 0 |
| Columbiana County | 99,823 | 17 | 4 | 1 |
| Coshocton County | 37,003 | 6 | 2 | 0 |
| Crawford County | 41,626 | 4 | 4 | 0 |
| Darke County | 51,462 | 11 | 4 | 1 |
| Delaware County | 237,966 | 3 | 0 | 0 |
| Fairfield County | 167,762 | 21 | 2 | 0 |
| Fayette County | 28,782 | 7 | 1 | 0 |
| Franklin County | 1,356,303 | 31 | 12 | 0 |
| Greene County | 172,347 | 17 | 2 | 0 |
| Guernsey County | 38,219 | 6 | 23 | 0 |
| Hamilton County | 837,359 | 12 | 2 | 0 |
| Hancock County | 75,016 | 8 | 19 | 0 |
| Hardin County | 30,402 | 8 | 5 | 0 |
| Harrison County | 14,042 | 15 | 17 | 0 |
| Holmes County | 44,668 | 11 | 8 | 3 |
| Huron County | 58,168 | 14 | 5 | 0 |
| Jefferson County | 63,900 | 18 | 17 | 0 |
| Knox County | 63,848 | 10 | 0 | 0 |
| Licking County | 184,898 | 22 | 0 | 0 |
| Logan County | 46,085 | 16 | 7 | 2 |
| Madison County | 45,531 | 17 | 6 | 0 |
| Marion County | 64,976 | 4 | 1 | 0 |
| Mercer County | 42,648 | 9 | 3 | 0 |
| Miami County | 111,950 | 16 | 7 | 1 |
| Montgomery County | 537,443 | 23 | 6 | 0 |
| Morrow County | 35,927 | 5 | 0 | 0 |
| Muskingum County | 86,582 | 11 | 37 | 0 |
| Perry County | 35,682 | 21 | 20 | 1 |
| Pickaway County | 62,158 | 20 | 8 | 3 |
| Pike County | 27,065 | 8 | 0 | 0 |
| Preble County | 40,801 | 12 | 2 | 0 |
| Richland County | 124,853 | 47 | 16 | 1 |
| Ross County | 76,046 | 7 | 2 | 0 |
| Seneca County | 54,730 | 11 | 20 | 0 |
| Shelby County | 47,952 | 16 | 2 | 0 |
| Stark County | 374,091 | 38 | 18 | 1 |
| Summit County | 538,370 | 31 | 9 | 0 |
| Tuscarawas County | 92,048 | 14 | 2 | 0 |
| Union County | 71,721 | 4 | 1 | 0 |
| Van Wert County | 28,887 | 5 | 10 | 0 |
| Warren County | 256,059 | 16 | 4 | 2 |
| Wayne County | 116,632 | 32 | 10 | 1 |
| Wyandot County | 21,394 | 4 | 0 | 0 |
Zone 2: moderate potential (35 counties)
| County | Residents | Water systems | Health violations since 2016 | Unresolved |
|---|---|---|---|---|
| Ashtabula County | 96,906 | 11 | 12 | 0 |
| Athens County | 63,218 | 13 | 16 | 0 |
| Brown County | 44,292 | 7 | 4 | 0 |
| Clermont County | 214,123 | 9 | 4 | 1 |
| Cuyahoga County | 1,240,594 | 7 | 0 | 0 |
| Defiance County | 38,644 | 9 | 98 | 0 |
| Erie County | 73,841 | 12 | 1 | 0 |
| Fulton County | 42,028 | 9 | 31 | 0 |
| Gallia County | 28,886 | 3 | 0 | 0 |
| Geauga County | 95,362 | 32 | 9 | 1 |
| Henry County | 27,536 | 10 | 38 | 0 |
| Highland County | 43,785 | 5 | 0 | 0 |
| Hocking County | 27,429 | 7 | 2 | 1 |
| Jackson County | 32,723 | 6 | 4 | 1 |
| Lake County | 232,360 | 6 | 1 | 0 |
| Lawrence County | 55,829 | 6 | 2 | 0 |
| Lorain County | 322,030 | 16 | 3 | 0 |
| Lucas County | 426,291 | 8 | 4 | 0 |
| Mahoning County | 225,786 | 11 | 9 | 0 |
| Medina County | 184,625 | 14 | 2 | 0 |
| Meigs County | 21,491 | 6 | 5 | 2 |
| Monroe County | 13,051 | 6 | 4 | 0 |
| Morgan County | 13,532 | 8 | 1 | 0 |
| Noble County | 14,269 | 6 | 3 | 0 |
| Ottawa County | 39,692 | 10 | 6 | 1 |
| Paulding County | 18,755 | 6 | 8 | 0 |
| Portage County | 163,839 | 32 | 3 | 0 |
| Putnam County | 34,206 | 10 | 16 | 0 |
| Sandusky County | 58,866 | 7 | 2 | 0 |
| Scioto County | 71,798 | 17 | 0 | 0 |
| Trumbull County | 200,300 | 26 | 22 | 1 |
| Vinton County | 12,545 | 3 | 18 | 0 |
| Washington County | 58,332 | 15 | 2 | 0 |
| Williams County | 36,554 | 13 | 3 | 0 |
| Wood County | 133,077 | 20 | 4 | 1 |
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
- Illinois
- Iowa
- Michigan
- Minnesota
- New Jersey
- New York
- 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.