Data release · August 21, 2026

US radon and air: the August 2026 data release

As of the August 21, 2026 release, 1,071 of the 3,143 US counties fall in EPA radon Zone 1, the highest of the three potential bands, home to about 85.9M people. Air quality is monitored in 1,012 counties, and the figures below read the worst of them for 2025. Every number is a federal figure or a count over federal rows; nothing is estimated or interpolated.

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1,071

Counties in radon Zone 1

of 3,143 counties

1,034

Counties in Zone 2

1,038

Counties in Zone 3

85.9M

People in a Zone 1 county

Radon by state

The states with the most Zone 1 counties

Ranked by the count of counties EPA maps in the highest radon potential zone. A zone describes the county, not any single home: houses above 4 pCi/L turn up in all three zones, so a test is the only way to know a specific address.

#	State	Zone 1	Zone 2	Zone 3	People in Zone 1
1	Iowa	99	0	0	3.2M
2	Minnesota	68	19	0	4.6M
3	Kansas	65	40	0	1.6M
4	Virginia	62	28	43	3.7M
5	Indiana	57	35	0	4.9M
6	Illinois	56	43	3	3.4M
7	Ohio	53	35	0	7.4M
8	Colorado	53	11	0	5.7M
9	Nebraska	53	24	16	1.6M
10	North Dakota	53	0	0	784k
11	Pennsylvania	49	17	1	10.0M
12	Montana	49	7	0	949k

EPA Map of Radon Zones, August 21, 2026 build. Zone 1 predicts an average indoor screening level above 4 pCi/L for the county as a whole.

Air quality 2025

The counties with the worst monitored air

Counties ranked by the number of days the Air Quality Index passed 100 in 2025, the point at which the EPA considers the air unhealthy for sensitive groups. A single year moves a long way in the West, where wildfire smoke drives it; the worst-counties page also carries the five-year average.

#	County	Above moderate	PM2.5 days	Median AQI	Max AQI
1	San Bernardino County, CA	110	125	77	207
2	Riverside County, CA	109	121	80	365
3	Los Angeles County, CA	98	151	74	201
4	Kern County, CA	65	153	70	200
5	El Paso County, TX	63	72	70	2,122
6	Doña Ana County, NM	48	122	61	528
7	Imperial County, CA	44	72	64	426
8	Tulare County, CA	43	163	64	147
9	Maricopa County, AZ	38	88	73	366
10	Harris County, TX	38	241	62	172
11	Pinal County, AZ	34	47	67	1,215
12	Fresno County, CA	34	151	61	164
13	San Diego County, CA	33	180	67	161
14	Tarrant County, TX	30	218	56	162
15	Clark County, NV	26	107	61	138

EPA Air Quality System annual summaries by county, 2025 (data spanning 2021 to 2025). A county appears only where a monitor reported; an unmonitored county is unmeasured, not clean.

What is in this release

Vintages behind the figures

Air quality (EPA AQS)	Annual summaries, 2021 to 2025
Respiratory prevalence (CDC PLACES)	PLACES 2022, 2023 (releases 2024, 2025)
Lung cancer death rate (NCI)	2019-2023
Lung cancer incidence (NCI)	2018-2022
Radon zones (EPA)	Current EPA Map of Radon Zones

More releases

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This is the earliest release on file.

Radon from the EPA Map of Radon Zones; air quality from the EPA Air Quality System. Lung.com sells home testing and remediation, not healthcare.