Indoor Air Quality • 5 min read • Last Updated October 28, 2026
EPA Radon Zones by County (Zones 1, 2 & 3): Complete Homebuyer Testing Guide
Compiled & Verified by: FullPropertyReport Environmental & Market Research Team
✓ ASTM & Federal Data Methodology
Primary Sources: U.S. EPA ECHO/RCRA/SDWIS • FEMA NFHL/NRI • USDA SSURGO • FHFA HPI • HUD SAFMR • U.S. Census
Understand the difference between EPA Radon Zone 1 (>4.0 pCi/L), Zone 2 (2.0–4.0 pCi/L), and Zone 3 (<2.0 pCi/L), and when to include a radon contingency in your offer.
How EPA Radon Zones Work
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. The U.S. EPA assigns every county to one of three zones: Zone 1 (High potential, predicted indoor screening level > 4.0 pCi/L), Zone 2 (Moderate potential, 2.0–4.0 pCi/L), and Zone 3 (Low potential, < 2.0 pCi/L). Every FullPropertyReport report includes your county's EPA Radon Zone designation.
Frequently Asked Questions
At what radon level does the EPA recommend mitigation?
The EPA recommends installing a radon mitigation system if indoor radon levels reach or exceed 4.0 picocuries per liter (pCi/L), and advises considering mitigation between 2.0 and 4.0 pCi/L.