EPA Zone 1

Where high radon potential meets the most people

1,071 of the 3,143 US counties are in EPA Radon Zone 1, the highest of three categories, where the predicted average indoor screening level is above the action level of 4 pCi/L. Radon coverage is usually organised by geology, which puts sparsely populated counties at the top.

Ranked by population instead, the list below shows where the largest number of people live above ground the EPA predicts is producing radon above the action level. It is a ranking of exposure, not of severity: every county here shares the same zone.

1,071

Zone 1 counties

34% of all US counties

85.9M

People in Zone 1 counties

Where CDC PLACES reports a population

4 pCi/L

EPA action level

Fix at or above

~21,000

US deaths a year

EPA estimate of radon-attributable lung cancer

Ranked by population

The 100 largest Zone 1 counties

#	County	Population	Smoking	COPD	Lung ca. deaths
1	Middlesex County, MA	1,623,952	9.1%	4.6%	26.1
2	Franklin County, OH	1,326,063	13.9%	6.3%	33.9
3	Hennepin County, MN	1,258,713	11.1%	4.4%	25.3
4	Allegheny County, PA	1,233,253	14.7%	7.2%	33.8
5	Fairfax County, VA	1,141,878	8.1%	4.1%	15.7
6	Fulton County, GA	1,079,105	9.9%	4.5%	25.6
7	Montgomery County, MD	1,058,474	7.2%	4.5%	16.8
8	Gwinnett County, GA	983,526	11.7%	5.0%	24.3
9	Marion County, IN	968,460	15.0%	7.3%	44.7
10	Erie County, NY	946,147	12.4%	6.9%	34.0
11	Worcester County, MA	866,866	12.3%	6.3%	32.1
12	Montgomery County, PA	864,683	12.5%	6.6%	26.8
13	Baltimore County, MD	844,703	11.1%	6.5%	33.8
14	Ventura County, CA	829,590	10.4%	5.2%	21.0
15	Hamilton County, OH	827,058	13.9%	7.1%	37.4
16	Essex County, MA	810,089	11.4%	6.3%	29.1
17	Cobb County, GA	776,743	10.4%	4.8%	24.3
18	Jefferson County, KY	773,399	16.4%	8.2%	41.6
19	DeKalb County, GA	762,992	11.5%	5.2%	21.8
20	El Paso County, CO	744,215	10.7%	5.2%	24.4
21	Jackson County, MO	718,560	15.8%	7.4%	37.6
22	Denver County, CO	716,577	10.3%	4.2%	22.2
23	Davidson County, TN	712,334	14.0%	6.2%	33.4
24	Bernalillo County, NM	671,586	12.0%	5.6%	19.8
25	Arapahoe County, CO	656,061	10.5%	4.9%	21.1
26	Bucks County, PA	645,054	15.5%	7.6%	28.9
27	Monmouth County, NJ	642,799	9.7%	5.0%	27.4
28	Johnson County, KS	622,237	9.7%	4.6%	24.3
29	Douglas County, NE	589,540	13.4%	5.6%	33.0
30	Jefferson County, CO	576,366	9.9%	5.0%	20.4
31	Dane County, WI	575,347	9.8%	4.4%	24.4
32	Delaware County, PA	575,182	12.5%	5.5%	33.7
33	Greenville County, SC	558,036	11.3%	6.4%	28.9
34	Lancaster County, PA	556,629	15.2%	7.3%	27.6
35	Spokane County, WA	551,455	11.7%	6.0%	31.2
36	Chester County, PA	545,823	10.6%	5.1%	26.1
37	Ramsey County, MN	536,075	12.5%	5.2%	28.6
38	Summit County, OH	535,733	14.6%	7.9%	37.2
39	Montgomery County, OH	533,796	15.2%	8.1%	39.7
40	Adams County, CO	533,365	13.4%	5.1%	25.6
41	Clark County, WA	521,150	11.0%	5.5%	31.5
42	Kane County, IL	514,982	11.0%	5.7%	27.8
43	Morris County, NJ	514,423	8.4%	4.2%	21.3
44	Polk County, IA	505,255	13.3%	5.8%	38.1
45	Knox County, TN	500,669	15.0%	7.4%	38.9
46	Onondaga County, NY	467,873	11.9%	6.8%	35.0
47	York County, PA	461,058	15.7%	6.5%	36.4
48	Dakota County, MN	447,440	11.3%	4.6%	24.5
49	Santa Barbara County, CA	441,257	10.7%	5.6%	20.2
50	Berks County, PA	430,449	14.8%	7.5%	31.4
51	Madison County, AL	412,600	11.8%	5.8%	31.1
52	Waukesha County, WI	412,591	10.3%	5.2%	27.3
53	Orange County, NY	407,470	12.0%	6.1%	32.5
54	Allen County, IN	394,545	14.4%	7.6%	36.4
55	Butler County, OH	393,043	14.6%	7.2%	39.5
56	Douglas County, CO	383,906	7.8%	4.0%	15.6
57	Chesterfield County, VA	383,876	11.5%	5.6%	30.8
58	Mercer County, NJ	381,671	10.5%	4.9%	24.6
59	Lehigh County, PA	376,317	16.0%	7.2%	30.0
60	Stark County, OH	372,716	17.1%	8.8%	38.6
61	Hamilton County, IN	371,645	9.5%	4.7%	23.8
62	Larimer County, CO	370,771	9.6%	5.2%	18.6
63	Rutherford County, TN	367,101	14.6%	6.2%	39.5
64	Washtenaw County, MI	365,536	9.8%	5.4%	25.9
65	Weld County, CO	359,442	12.7%	5.5%	22.6
66	Westmoreland County, PA	352,057	13.4%	7.0%	33.6
67	Somerset County, NJ	348,842	8.2%	4.1%	20.6
68	Howard County, MD	336,001	7.4%	4.0%	19.5
69	Boulder County, CO	326,831	8.8%	4.7%	16.5
70	Lancaster County, NE	326,716	11.7%	5.5%	30.0
71	Luzerne County, PA	326,369	17.5%	8.5%	38.5
72	Fayette County, KY	320,347	15.4%	7.7%	33.8
73	Northampton County, PA	318,526	14.6%	6.9%	29.2
74	Albany County, NY	316,659	10.5%	5.7%	31.0
75	Cumberland County, ME	310,230	10.9%	6.1%	31.9
76	Dutchess County, NY	297,150	11.0%	5.9%	29.3
77	Frederick County, MD	293,391	9.2%	5.1%	25.8
78	Dauphin County, PA	288,800	17.1%	7.9%	30.4
79	Winnebago County, IL	280,922	15.5%	8.3%	38.3
80	Washington County, MN	278,936	10.9%	4.5%	25.3
81	Buncombe County, NC	275,901	12.3%	6.9%	28.5
82	St. Joseph County, IN	272,848	14.9%	7.8%	39.0
83	Cumberland County, PA	268,579	14.1%	6.9%	30.7
84	Harford County, MD	264,644	10.9%	6.1%	34.8
85	Williamson County, TN	264,460	10.4%	5.2%	21.5
86	Kalamazoo County, MI	262,215	12.9%	6.9%	35.5
87	Clay County, MO	259,772	14.2%	6.4%	38.0
88	Warren County, OH	252,148	12.2%	5.8%	32.7
89	Delaware County, OH	231,636	10.1%	4.9%	25.3
90	Linn County, IA	228,972	13.5%	6.5%	34.7
91	York County, ME	218,586	13.4%	7.8%	36.5
92	Lackawanna County, PA	215,615	16.5%	8.1%	38.1
93	Minnehaha County, SD	206,930	14.2%	5.6%	43.6
94	Elkhart County, IN	206,409	17.0%	8.8%	36.6
95	Champaign County, IL	205,644	11.1%	5.6%	29.0
96	Sarpy County, NE	199,886	11.1%	4.6%	32.3
97	Butler County, PA	197,300	12.2%	6.2%	30.6
98	Cass County, ND	196,362	11.2%	4.5%	31.4
99	Broome County, NY	196,077	13.2%	7.7%	32.7
100	Sangamon County, IL	193,491	13.2%	7.3%	37.6

Zones from the EPA Map of Radon Zones. Population, smoking and COPD from CDC PLACES. Lung cancer death rates are age-adjusted deaths per 100,000 per year, 2019-2023, from NCI State Cancer Profiles. Being high on this list means a county is populous, not that its radon is worse than another Zone 1 county’s.

Where the risks compound

Zone 1 counties with the highest smoking rates

Radon and tobacco smoke do not simply add up. The EPA’s own risk tables put a smoker exposed to 4 pCi/L at several times the lifetime lung cancer risk of a never-smoker at the same level. These are the Zone 1 counties above 50,000 residents where the largest share of adults currently smoke.

County	Adults who smoke	Population	Lung ca. deaths
Pulaski County, KY	22.6%	65,795	54.7
Hawkins County, TN	21.2%	58,600	55.5
Mercer County, WV	21.1%	58,057	45.7
Hamblen County, TN	20.9%	66,216	49.7
Greene County, TN	20.6%	72,577	50.7
Clearfield County, PA	20.0%	77,904	34.7
Schuylkill County, PA	19.9%	143,104	43.3
Ross County, OH	19.8%	76,501	51.0
Somerset County, ME	19.7%	51,302	56.1
McMinn County, TN	19.7%	55,678	54.7
Marion County, OH	19.6%	64,851	45.2
Armstrong County, PA	19.6%	64,747	40.3
Bedford County, TN	19.4%	53,055	57.1
Bullitt County, KY	19.2%	83,836	43.0
Blair County, PA	19.2%	121,032	38.2
Northumberland County, PA	19.2%	90,133	37.1
Sullivan County, TN	19.2%	162,135	48.7
Wayne County, IN	19.1%	66,127	44.7
Jackson County, AL	19.0%	53,467	53.5
Roane County, TN	18.9%	56,096	44.4

Smoking prevalence is a CDC PLACES model-based estimate of the share of adults who currently smoke cigarettes. Putting it next to the radon zone describes two risks present in the same population; it does not claim one causes the other.