Which states have the highest radon levels?

Iowa, North Dakota, and Minnesota consistently have the highest average radon levels in the United States. South Dakota, Pennsylvania, Nebraska, and Colorado also rank among the highest. Over 40–70% of homes in these states test above the EPA action level of 4.0 pCi/L.

Which states have the lowest radon levels?

Hawaii has by far the lowest radon levels in the US due to its volcanic basalt geology. Florida, Louisiana, and Mississippi also have very low levels due to their flat, alluvial, and coastal plain geology.

State-by-State Radon Guide

Radon Levels by State

Radon levels vary significantly across the United States, driven by local geology, soil composition, and building practices. Use this guide to understand your state's risk level and find specific information for your area.

Very High Risk: 5 statesHigh Risk: 22 statesModerate Risk: 13 statesLow Risk: 10 states

Every Home Should Be Tested — Regardless of State Risk Level

State averages and EPA zone maps reflect broad geological trends, but individual homes within any state can vary dramatically. Two homes on the same street can have radon levels that differ by 10x. The only way to know your home's actual level is to test. EPA estimates that 1 in 15 US homes has elevated radon — including in low-risk states.

State	Risk Level	EPA Zone	Avg. Radon	% Homes > 4 pCi/L
IAIowa	Very High Risk	Zone 1	5–10 pCi/L	71%	Details
MNMinnesota	Very High Risk	Zone 1	3–8 pCi/L	40%	Details
NDNorth Dakota	Very High Risk	Zone 1	4–10 pCi/L	65%	Details
PAPennsylvania	Very High Risk	Zone 1	4–9 pCi/L	41%	Details
SDSouth Dakota	Very High Risk	Zone 1	3–9 pCi/L	47%	Details
COColorado	High Risk	Zone 1	2–8 pCi/L	45%	Details
CTConnecticut	High Risk	Zone 1	2–6 pCi/L	28%	Details
IDIdaho	High Risk	Zone 1	2–7 pCi/L	35%	Details
ILIllinois	High Risk	Zone 1	2–6 pCi/L	30%	Details
INIndiana	High Risk	Zone 1	2–6 pCi/L	35%	Details
KSKansas	High Risk	Zone 1	2–6 pCi/L	32%	Details
KYKentucky	High Risk	Zone 1	2–7 pCi/L	36%	Details
MEMaine	High Risk	Zone 1	2–6 pCi/L	32%	Details
MAMassachusetts	High Risk	Zone 1	2–6 pCi/L	29%	Details
MOMissouri	High Risk	Zone 1	2–6 pCi/L	33%	Details
MTMontana	High Risk	Zone 1	2–8 pCi/L	38%	Details
NENebraska	High Risk	Zone 1	3–7 pCi/L	47%	Details
NHNew Hampshire	High Risk	Zone 1	2–7 pCi/L	38%	Details
NJNew Jersey	High Risk	Zone 1	2–6 pCi/L	32%	Details
NYNew York	High Risk	Zone 1	2–6 pCi/L	30%	Details
OHOhio	High Risk	Zone 1	2–6 pCi/L	31%	Details
UTUtah	High Risk	Zone 1	2–6 pCi/L	29%	Details
VTVermont	High Risk	Zone 1	2–6 pCi/L	30%	Details
VAVirginia	High Risk	Zone 1	2–6 pCi/L	27%	Details
WVWest Virginia	High Risk	Zone 1	2–7 pCi/L	35%	Details
WIWisconsin	High Risk	Zone 1	3–7 pCi/L	37%	Details
WYWyoming	High Risk	Zone 1	2–7 pCi/L	33%	Details
AKAlaska	Moderate Risk	Zone 2	1–4.5 pCi/L	18%	Details
AZArizona	Moderate Risk	Zone 2	1–3.5 pCi/L	11%	Details
DEDelaware	Moderate Risk	Zone 2	1.5–4.5 pCi/L	20%	Details
MDMaryland	Moderate Risk	Zone 2	1.5–5.5 pCi/L	24%	Details
MIMichigan	Moderate Risk	Zone 2	1–4 pCi/L	18%	Details
NVNevada	Moderate Risk	Zone 2	1–3.5 pCi/L	10%	Details
NMNew Mexico	Moderate Risk	Zone 2	1–4.5 pCi/L	14%	Details
NCNorth Carolina	Moderate Risk	Zone 2	1–4.5 pCi/L	14%	Details
OKOklahoma	Moderate Risk	Zone 2	1–4 pCi/L	12%	Details
OROregon	Moderate Risk	Zone 2	1–4 pCi/L	13%	Details
RIRhode Island	Moderate Risk	Zone 2	1.5–4.5 pCi/L	16%	Details
TNTennessee	Moderate Risk	Zone 2	1–4.5 pCi/L	14%	Details
WAWashington	Moderate Risk	Zone 2	1–4 pCi/L	11%	Details
ALAlabama	Low Risk	Zone 3	0.4–2 pCi/L	4%	Details
ARArkansas	Low Risk	Zone 3	0.4–2 pCi/L	5%	Details
CACalifornia	Low Risk	Zone 3	0.5–2.5 pCi/L	6%	Details
FLFlorida	Low Risk	Zone 3	0.2–1.2 pCi/L	2%	Details
GAGeorgia	Low Risk	Zone 3	0.5–3 pCi/L	7%	Details
HIHawaii	Low Risk	Zone 3	0.2–0.6 pCi/L	1%	Details
LALouisiana	Low Risk	Zone 3	0.2–1 pCi/L	2%	Details
MSMississippi	Low Risk	Zone 3	0.2–1 pCi/L	2%	Details
SCSouth Carolina	Low Risk	Zone 3	0.5–3 pCi/L	7%	Details
TXTexas	Low Risk	Zone 3	0.5–2.5 pCi/L	6%	Details

Understanding EPA Radon Zones

Zone 1

High Risk

Predicted average indoor radon level greater than 4 pCi/L. The EPA estimates that homes in these counties have the highest radon potential. Radon-resistant new construction is strongly recommended.

Zone 2

Moderate Risk

Predicted average indoor radon level from 2–4 pCi/L. Testing is recommended for all homes in these counties, and mitigation should follow any test above 4 pCi/L.

Zone 3

Low Risk

Predicted average indoor radon level less than 2 pCi/L. Testing is still recommended — individual homes can still test above the action level regardless of zone classification.

Source: EPA Radon Zone Map. Note: Zone classifications are county-level averages based on geological data. Individual homes can have significantly different levels.

Radon Levels by State

Every Home Should Be Tested — Regardless of State Risk Level

Radon Guides by City

Understanding EPA Radon Zones