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 139 cities.

Updated August 30, 2026

Highest city

8.1pCi/L

Northwest Harwinton

Connecticut city average

2.3pCi/L

across 139 cities

Above action level

12/ 139

cities

Connecticut Cities Ranked by Indoor Radon Levels
#	Location	Avg level	vs action level
1	Northwest Harwinton	8.1 pCi/L	2.0× over
2	Derby	6.8 pCi/L	1.7× over
3	Ansonia	6.0 pCi/L	1.5× over
4	Montville Center	5.5 pCi/L	1.4× over
5	Old Mystic	5.3 pCi/L	1.3× over
6	Danielson	5.0 pCi/L	1.3× over
7	East Hampton	5.0 pCi/L	1.2× over
8	Cos Cob	4.6 pCi/L	1.2× over
9	New Hartford Center	4.3 pCi/L	1.1× over
10	South Woodstock	4.3 pCi/L	1.1× over
11	Windham	4.3 pCi/L	1.1× over
12	Madison Center	4.0 pCi/L	1.0× over
✓ Below EPA action level (4 pCi/L)
13	Branford Center	3.8 pCi/L	1.0× under
14	Georgetown	3.7 pCi/L	0.9× under
15	Heritage Village	3.6 pCi/L	0.9× under
16	Seymour	3.6 pCi/L	0.9× under
17	Woodmont	3.5 pCi/L	0.9× under
18	Durham	3.3 pCi/L	0.8× under
19	Jewett City	3.2 pCi/L	0.8× under
20	Windsor Locks	3.1 pCi/L	0.8× under
21	Wolcott	3.1 pCi/L	0.8× under
22	Woodbury Center	3.1 pCi/L	0.8× under
23	Prospect	3.1 pCi/L	0.8× under
24	Clinton	3.0 pCi/L	0.8× under
25	West Torrington	3.0 pCi/L	0.8× under
26	North Branford	3.0 pCi/L	0.7× under
27	Central Waterford	2.9 pCi/L	0.7× under
28	New Milford	2.9 pCi/L	0.7× under
29	Plainfield	2.9 pCi/L	0.7× under
30	Lake Pocotopaug	2.9 pCi/L	0.7× under
31	City of Milford (balance)	2.9 pCi/L	0.7× under
32	Ledyard Center	2.8 pCi/L	0.7× under
33	Pawcatuck	2.8 pCi/L	0.7× under
34	Ellington	2.7 pCi/L	0.7× under
35	New Preston	2.7 pCi/L	0.7× under
36	Norwich	2.7 pCi/L	0.7× under
37	Oxford	2.7 pCi/L	0.7× under
38	Southbury	2.6 pCi/L	0.7× under
39	Kent	2.6 pCi/L	0.7× under
40	Sherman	2.6 pCi/L	0.7× under
41	Colchester	2.5 pCi/L	0.6× under
42	Cromwell	2.5 pCi/L	0.6× under
43	Wilton	2.5 pCi/L	0.6× under
44	Farmington	2.5 pCi/L	0.6× under
45	Guilford	2.5 pCi/L	0.6× under
46	Bethlehem Village	2.5 pCi/L	0.6× under
47	Southport	2.4 pCi/L	0.6× under
48	North Haven	2.4 pCi/L	0.6× under
49	Baltic	2.4 pCi/L	0.6× under
50	Moosup	2.4 pCi/L	0.6× under
51	Waterbury	2.4 pCi/L	0.6× under
52	Middlebury	2.4 pCi/L	0.6× under
53	Torrington	2.3 pCi/L	0.6× under
54	Shelton	2.3 pCi/L	0.6× under
55	Winsted	2.3 pCi/L	0.6× under
56	Terryville	2.3 pCi/L	0.6× under
57	Newtown	2.3 pCi/L	0.6× under
58	Tariffville	2.3 pCi/L	0.6× under
59	Stamford	2.3 pCi/L	0.6× under
60	Middletown	2.3 pCi/L	0.6× under
61	Orange	2.2 pCi/L	0.6× under
62	Preston City	2.2 pCi/L	0.6× under
63	Oakville	2.2 pCi/L	0.6× under
64	Trumbull	2.2 pCi/L	0.6× under
65	Niantic	2.2 pCi/L	0.5× under
66	Wallingford	2.2 pCi/L	0.5× under
67	Bridgeport	2.2 pCi/L	0.5× under
68	Stratford	2.2 pCi/L	0.5× under
69	Old Saybrook Center	2.1 pCi/L	0.5× under
70	East Haven	2.1 pCi/L	0.5× under
71	Westport	2.1 pCi/L	0.5× under
72	Glenville	2.1 pCi/L	0.5× under
73	Wethersfield	2.1 pCi/L	0.5× under
74	East Norwalk	2.0 pCi/L	0.5× under
75	Riverside	2.0 pCi/L	0.5× under
76	Ridgefield	2.0 pCi/L	0.5× under
77	Cheshire Village	2.0 pCi/L	0.5× under
78	Canaan	1.9 pCi/L	0.5× under
79	Meriden	1.9 pCi/L	0.5× under
80	Hamden	1.9 pCi/L	0.5× under
81	Milford	1.9 pCi/L	0.5× under
82	Fairfield	1.9 pCi/L	0.5× under
83	Willimantic	1.9 pCi/L	0.5× under
84	Darien	1.8 pCi/L	0.5× under
85	Hebron	1.8 pCi/L	0.5× under
86	Higganum	1.8 pCi/L	0.5× under
87	North Stamford	1.8 pCi/L	0.5× under
88	Tolland	1.8 pCi/L	0.5× under
89	Greenwich	1.8 pCi/L	0.5× under
90	Kensington	1.8 pCi/L	0.5× under
91	Collinsville	1.8 pCi/L	0.5× under
92	Canton Valley	1.8 pCi/L	0.4× under
93	Danbury	1.7 pCi/L	0.4× under
94	Simsbury Center	1.7 pCi/L	0.4× under
95	Watertown	1.7 pCi/L	0.4× under
96	Coventry Lake	1.7 pCi/L	0.4× under
97	Norwalk	1.7 pCi/L	0.4× under
98	Groton	1.7 pCi/L	0.4× under
99	New Canaan	1.7 pCi/L	0.4× under
100	Old Greenwich	1.6 pCi/L	0.4× under
101	Mansfield City	1.6 pCi/L	0.4× under
102	Gales Ferry	1.6 pCi/L	0.4× under
103	Manchester	1.6 pCi/L	0.4× under
104	Plainville	1.6 pCi/L	0.4× under
105	Bristol	1.6 pCi/L	0.4× under
106	Woodbridge	1.6 pCi/L	0.4× under
107	Storrs	1.5 pCi/L	0.4× under
108	Bethel	1.5 pCi/L	0.4× under
109	North Granby	1.5 pCi/L	0.4× under
110	Glastonbury Center	1.5 pCi/L	0.4× under
111	Blue Hills	1.4 pCi/L	0.3× under
112	Long Hill	1.4 pCi/L	0.3× under
113	New Haven	1.4 pCi/L	0.3× under
114	Newington	1.4 pCi/L	0.3× under
115	Rockville	1.4 pCi/L	0.3× under
116	Deep River Center	1.3 pCi/L	0.3× under
117	Madison	1.3 pCi/L	0.3× under
118	Suffield Depot	1.3 pCi/L	0.3× under
119	Weatogue	1.3 pCi/L	0.3× under
120	Terramuggus	1.3 pCi/L	0.3× under
121	Mystic	1.3 pCi/L	0.3× under
122	Salmon Brook	1.2 pCi/L	0.3× under
123	Wallingford Center	1.2 pCi/L	0.3× under
124	Essex Village	1.2 pCi/L	0.3× under
125	Poquonock Bridge	1.1 pCi/L	0.3× under
126	West Hartford	1.1 pCi/L	0.3× under
127	Cheshire	1.1 pCi/L	0.3× under
128	East Hartford	1.1 pCi/L	0.3× under
129	Litchfield	1.1 pCi/L	0.3× under
130	Naugatuck	1.0 pCi/L	0.3× under
131	Moodus	1.0 pCi/L	0.3× under
132	New Britain	0.9 pCi/L	0.2× under
133	Branford	0.8 pCi/L	0.2× under
134	Pemberwick	0.8 pCi/L	0.2× under
135	South Coventry	0.8 pCi/L	0.2× under
136	Glastonbury	0.8 pCi/L	0.2× under
137	West Haven	0.8 pCi/L	0.2× under
138	South Windsor	0.6 pCi/L	0.2× under
139	Hartford	0.6 pCi/L	0.1× under

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