Ohio Radon Levels
53Zone 1 (High)
35Zone 2 (Moderate)
0Zone 3 (Low)
60% of counties in Ohio 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 |
| Allen County | Zone 1 | Highest Potential |
| Ashland County | Zone 1 | Highest Potential |
| Ashtabula County | Zone 2 | Moderate Potential |
| Athens County | Zone 2 | Moderate Potential |
| Auglaize County | Zone 1 | Highest Potential |
| Belmont County | Zone 1 | Highest Potential |
| Brown County | Zone 2 | Moderate Potential |
| Butler County | Zone 1 | Highest Potential |
| Carroll County | Zone 1 | Highest Potential |
| Champaign County | Zone 1 | Highest Potential |
| Clark County | Zone 1 | Highest Potential |
| Clermont County | Zone 2 | Moderate Potential |
| Clinton County | Zone 1 | Highest Potential |
| Columbiana County | Zone 1 | Highest Potential |
| Coshocton County | Zone 1 | Highest Potential |
| Crawford County | Zone 1 | Highest Potential |
| Cuyahoga County | Zone 2 | Moderate Potential |
| Darke County | Zone 1 | Highest Potential |
| Defiance County | Zone 2 | Moderate Potential |
| Delaware County | Zone 1 | Highest Potential |
| Erie County | Zone 2 | Moderate Potential |
| Fairfield County | Zone 1 | Highest Potential |
| Fayette County | Zone 1 | Highest Potential |
| Franklin County | Zone 1 | Highest Potential |
| Fulton County | Zone 2 | Moderate Potential |
| Gallia County | Zone 2 | Moderate Potential |
| Geauga County | Zone 2 | Moderate Potential |
| Greene County | Zone 1 | Highest Potential |
| Guernsey County | Zone 1 | Highest Potential |
| Hamilton County | Zone 1 | Highest Potential |
| Hancock County | Zone 1 | Highest Potential |
| Hardin County | Zone 1 | Highest Potential |
| Harrison County | Zone 1 | Highest Potential |
| Henry County | Zone 2 | Moderate Potential |
| Highland County | Zone 2 | Moderate Potential |
| Hocking County | Zone 2 | Moderate Potential |
| Holmes County | Zone 1 | Highest Potential |
| Huron County | Zone 1 | Highest Potential |
| Jackson County | Zone 2 | Moderate Potential |
| Jefferson County | Zone 1 | Highest Potential |
| Knox County | Zone 1 | Highest Potential |
| Lake County | Zone 2 | Moderate Potential |
| Lawrence County | Zone 2 | Moderate Potential |
| Licking County | Zone 1 | Highest Potential |
| Logan County | Zone 1 | Highest Potential |
| Lorain County | Zone 2 | Moderate Potential |
| Lucas County | Zone 2 | Moderate Potential |
| Madison County | Zone 1 | Highest Potential |
| Mahoning County | Zone 2 | Moderate Potential |
| Marion County | Zone 1 | Highest Potential |
| Medina County | Zone 2 | Moderate Potential |
| Meigs County | Zone 2 | Moderate Potential |
| Mercer County | Zone 1 | Highest Potential |
| Miami County | Zone 1 | Highest Potential |
| Monroe County | Zone 2 | Moderate Potential |
| Montgomery County | Zone 1 | Highest Potential |
| Morgan County | Zone 2 | Moderate Potential |
| Morrow County | Zone 1 | Highest Potential |
| Muskingum County | Zone 1 | Highest Potential |
| Noble County | Zone 2 | Moderate Potential |
| Ottawa County | Zone 2 | Moderate Potential |
| Paulding County | Zone 2 | Moderate Potential |
| Perry County | Zone 1 | Highest Potential |
| Pickaway County | Zone 1 | Highest Potential |
| Pike County | Zone 1 | Highest Potential |
| Portage County | Zone 2 | Moderate Potential |
| Preble County | Zone 1 | Highest Potential |
| Putnam County | Zone 2 | Moderate Potential |
| Richland County | Zone 1 | Highest Potential |
| Ross County | Zone 1 | Highest Potential |
| Sandusky County | Zone 2 | Moderate Potential |
| Scioto County | Zone 2 | Moderate Potential |
| Seneca County | Zone 1 | Highest Potential |
| Shelby County | Zone 1 | Highest Potential |
| Stark County | Zone 1 | Highest Potential |
| Summit County | Zone 1 | Highest Potential |
| Trumbull County | Zone 2 | Moderate Potential |
| Tuscarawas County | Zone 1 | Highest Potential |
| Union County | Zone 1 | Highest Potential |
| Van Wert County | Zone 1 | Highest Potential |
| Vinton County | Zone 2 | Moderate Potential |
| Warren County | Zone 1 | Highest Potential |
| Washington County | Zone 2 | Moderate Potential |
| Wayne County | Zone 1 | Highest Potential |
| Williams County | Zone 2 | Moderate Potential |
| Wood County | Zone 2 | Moderate Potential |
| Wyandot County | Zone 1 | Highest Potential |