Direct answer
Ohio sits atop limestone and shale geology that releases radon as uranium decays. Hamilton, Butler, Warren, and Clermont counties are all designated EPA Radon Zone 1 (the highest classification), meaning average indoor levels exceed 4.0 pCi/L.
Authoritative sources
Cincinnati and surrounding counties sit in EPA Radon Zone 1, the highest-risk classification.
EPA recommends mitigation above 4.0 pCi/L and consideration of mitigation between 2.0 and 4.0 pCi/L.
Ohio Radon Program guidance on testing, mitigation, and contractor licensure.
Related questions
We connect Greater Cincinnati homeowners with NRPP-credentialed radon mitigators in our partner network. Mon-Sat 8am-7pm.
