Connecticut Cities Ranked by Indoor Radon Levels

Measured averages from Airthings devices across Connecticut, USA. Action level: 4 pCi/L — the threshold at which remediation is recommended.

Northwest Harwinton has the highest measured indoor radon in Connecticut at 8.1 pCi/L, based on Airthings measurements across 134 cities.

Updated August 16, 2026

Highest city

8.1pCi/L

Northwest Harwinton

Connecticut city average

2.3pCi/L

across 134 cities

Above action level

11/ 134

cities

Connecticut Cities Ranked by Indoor Radon Levels
#	Location	Avg level	Monitors	vs action level
1	Northwest Harwinton	8.1 pCi/L	7	2.0× over
2	Ansonia	6.0 pCi/L	7	1.5× over
3	Montville Center	5.5 pCi/L	12	1.4× over
4	Old Mystic	5.3 pCi/L	17	1.3× over
5	Danielson	5.0 pCi/L	7	1.3× over
6	East Hampton	5.0 pCi/L	12	1.2× over
7	Cos Cob	4.6 pCi/L	52	1.2× over
8	New Hartford Center	4.3 pCi/L	10	1.1× over
9	South Woodstock	4.3 pCi/L	9	1.1× over
10	Windham	4.3 pCi/L	7	1.1× over
11	Madison Center	4.0 pCi/L	14	1.0× over
✓ Below EPA action level (4 pCi/L)
12	Branford Center	3.8 pCi/L	12	1.0× under
13	Georgetown	3.7 pCi/L	57	0.9× under
14	Heritage Village	3.6 pCi/L	11	0.9× under
15	Seymour	3.6 pCi/L	16	0.9× under
16	Woodmont	3.5 pCi/L	6	0.9× under
17	Durham	3.3 pCi/L	21	0.8× under
18	Jewett City	3.2 pCi/L	10	0.8× under
19	Windsor Locks	3.1 pCi/L	9	0.8× under
20	Wolcott	3.1 pCi/L	24	0.8× under
21	Prospect	3.1 pCi/L	13	0.8× under
22	Clinton	3.0 pCi/L	11	0.8× under
23	West Torrington	3.0 pCi/L	8	0.8× under
24	North Branford	3.0 pCi/L	17	0.7× under
25	Central Waterford	2.9 pCi/L	6	0.7× under
26	New Milford	2.9 pCi/L	29	0.7× under
27	Plainfield	2.9 pCi/L	7	0.7× under
28	Lake Pocotopaug	2.9 pCi/L	7	0.7× under
29	City of Milford (balance)	2.9 pCi/L	19	0.7× under
30	Ledyard Center	2.8 pCi/L	13	0.7× under
31	Pawcatuck	2.8 pCi/L	21	0.7× under
32	Ellington	2.7 pCi/L	10	0.7× under
33	New Preston	2.7 pCi/L	17	0.7× under
34	Norwich	2.7 pCi/L	16	0.7× under
35	Oxford	2.7 pCi/L	34	0.7× under
36	Southbury	2.6 pCi/L	22	0.7× under
37	Kent	2.6 pCi/L	13	0.7× under
38	Sherman	2.6 pCi/L	12	0.7× under
39	Colchester	2.5 pCi/L	15	0.6× under
40	Cromwell	2.5 pCi/L	19	0.6× under
41	Wilton	2.5 pCi/L	100	0.6× under
42	Farmington	2.5 pCi/L	37	0.6× under
43	Guilford	2.5 pCi/L	32	0.6× under
44	Bethlehem Village	2.5 pCi/L	9	0.6× under
45	Southport	2.4 pCi/L	56	0.6× under
46	North Haven	2.4 pCi/L	13	0.6× under
47	Baltic	2.4 pCi/L	12	0.6× under
48	Moosup	2.4 pCi/L	12	0.6× under
49	Waterbury	2.4 pCi/L	12	0.6× under
50	Middlebury	2.4 pCi/L	9	0.6× under
51	Torrington	2.3 pCi/L	8	0.6× under
52	Shelton	2.3 pCi/L	42	0.6× under
53	Winsted	2.3 pCi/L	7	0.6× under
54	Terryville	2.3 pCi/L	7	0.6× under
55	Newtown	2.3 pCi/L	65	0.6× under
56	Tariffville	2.3 pCi/L	6	0.6× under
57	Stamford	2.3 pCi/L	100	0.6× under
58	Middletown	2.3 pCi/L	21	0.6× under
59	Orange	2.2 pCi/L	34	0.6× under
60	Oakville	2.2 pCi/L	16	0.6× under
61	Trumbull	2.2 pCi/L	119	0.6× under
62	Niantic	2.2 pCi/L	28	0.5× under
63	Wallingford	2.2 pCi/L	20	0.5× under
64	Bridgeport	2.2 pCi/L	39	0.5× under
65	Stratford	2.2 pCi/L	32	0.5× under
66	Old Saybrook Center	2.1 pCi/L	9	0.5× under
67	East Haven	2.1 pCi/L	12	0.5× under
68	Westport	2.1 pCi/L	148	0.5× under
69	Glenville	2.1 pCi/L	30	0.5× under
70	Wethersfield	2.1 pCi/L	36	0.5× under
71	East Norwalk	2.0 pCi/L	16	0.5× under
72	Riverside	2.0 pCi/L	59	0.5× under
73	Ridgefield	2.0 pCi/L	77	0.5× under
74	Cheshire Village	2.0 pCi/L	18	0.5× under
75	Canaan	1.9 pCi/L	7	0.5× under
76	Meriden	1.9 pCi/L	22	0.5× under
77	Hamden	1.9 pCi/L	45	0.5× under
78	Milford	1.9 pCi/L	7	0.5× under
79	Fairfield	1.9 pCi/L	47	0.5× under
80	North Stamford	1.9 pCi/L	63	0.5× under
81	Willimantic	1.9 pCi/L	6	0.5× under
82	Darien	1.8 pCi/L	68	0.5× under
83	Hebron	1.8 pCi/L	15	0.5× under
84	Higganum	1.8 pCi/L	12	0.5× under
85	Tolland	1.8 pCi/L	12	0.5× under
86	Greenwich	1.8 pCi/L	51	0.5× under
87	Kensington	1.8 pCi/L	23	0.5× under
88	Collinsville	1.8 pCi/L	27	0.5× under
89	Canton Valley	1.8 pCi/L	22	0.4× under
90	Danbury	1.7 pCi/L	45	0.4× under
91	Simsbury Center	1.7 pCi/L	17	0.4× under
92	Watertown	1.7 pCi/L	12	0.4× under
93	Coventry Lake	1.7 pCi/L	9	0.4× under
94	Norwalk	1.7 pCi/L	71	0.4× under
95	Groton	1.7 pCi/L	6	0.4× under
96	New Canaan	1.7 pCi/L	59	0.4× under
97	Old Greenwich	1.6 pCi/L	12	0.4× under
98	Mansfield City	1.6 pCi/L	7	0.4× under
99	Gales Ferry	1.6 pCi/L	7	0.4× under
100	Manchester	1.6 pCi/L	40	0.4× under
101	Plainville	1.6 pCi/L	43	0.4× under
102	Bristol	1.6 pCi/L	30	0.4× under
103	Woodbridge	1.6 pCi/L	37	0.4× under
104	Storrs	1.5 pCi/L	13	0.4× under
105	Bethel	1.5 pCi/L	47	0.4× under
106	North Granby	1.5 pCi/L	12	0.4× under
107	Glastonbury Center	1.5 pCi/L	50	0.4× under
108	Blue Hills	1.4 pCi/L	14	0.3× under
109	New Haven	1.4 pCi/L	30	0.3× under
110	Newington	1.4 pCi/L	25	0.3× under
111	Rockville	1.4 pCi/L	22	0.3× under
112	Deep River Center	1.3 pCi/L	11	0.3× under
113	Madison	1.3 pCi/L	15	0.3× under
114	Suffield Depot	1.3 pCi/L	10	0.3× under
115	Weatogue	1.3 pCi/L	15	0.3× under
116	Terramuggus	1.3 pCi/L	25	0.3× under
117	Mystic	1.3 pCi/L	13	0.3× under
118	Salmon Brook	1.2 pCi/L	8	0.3× under
119	Wallingford Center	1.2 pCi/L	10	0.3× under
120	Essex Village	1.2 pCi/L	15	0.3× under
121	Poquonock Bridge	1.1 pCi/L	8	0.3× under
122	West Hartford	1.1 pCi/L	50	0.3× under
123	Cheshire	1.1 pCi/L	8	0.3× under
124	East Hartford	1.1 pCi/L	6	0.3× under
125	Litchfield	1.1 pCi/L	10	0.3× under
126	Naugatuck	1.0 pCi/L	7	0.3× under
127	Moodus	1.0 pCi/L	10	0.3× under
128	New Britain	0.9 pCi/L	8	0.2× under
129	Branford	0.8 pCi/L	12	0.2× under
130	Pemberwick	0.8 pCi/L	6	0.2× under
131	South Coventry	0.8 pCi/L	10	0.2× under
132	Glastonbury	0.8 pCi/L	7	0.2× under
133	South Windsor	0.6 pCi/L	6	0.2× under
134	Hartford	0.6 pCi/L	11	0.1× under

See USA cities ranked by radon level See all States ranked by radon level