Radon Levels by State: Where the High-Radon Ground Is

Radon risk in the US is geological, and geology doesn’t follow state lines neatly — but state-level patterns are real and strong. The upper Midwest, the northern Plains, the Rockies, and much of Appalachia and New England sit on uranium-bearing rock and glacial soils that push predicted indoor radon at or above the EPA’s 4 pCi/L action level. The Gulf Coast and Deep South largely don’t.

The table below shows the predominant EPA radon zone for every state — the same dataset our address reports draw from. Remember the standard caveat: the zone predicts the regional average; only a test tells you about a specific house.

EPA radon zones, state by state

Zone 1 = predicted average ≥ 4 pCi/L (high) · Zone 2 = 2–4 pCi/L (moderate) · Zone 3 = < 2 pCi/L (low). State entries show the predominant zone; individual counties within a state can differ — check your county through any state link.

How to read this if you're house-hunting

• In a Zone 1 state (Iowa, North Dakota, Colorado, Ohio, Pennsylvania…): assume testing is a standard part of any purchase. Half or more of homes in many Zone 1 counties test above the action level. Our Zone 1 guide covers the negotiation playbook.
• In a Zone 2 state: the regional average is moderate, but Zone 1 counties hide inside most Zone 2 states — county granularity matters most here.
• In a Zone 3 state (Florida, Louisiana, Hawaii…): the odds are friendlier, but elevated houses exist in every state, and the test is still the only way to know. The EPA recommends testing every home regardless of zone.

What the numbers on a test result mean — and when to act — is covered in acceptable radon levels.

Why the cold states dominate the high-radon list

Two compounding reasons. First, geology: glaciated soils and uranium-rich bedrock concentrate in the northern US and the mountain West. Second, behavior: cold-climate homes are sealed tight and run heating systems that depressurize lower levels, actively pulling soil gas indoors — the same house, picked up and moved south, would test lower. It’s also why winter test results run higher than summer ones everywhere.