Delaware Cities Ranked by Indoor Radon Levels

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

Bethany Beach has the highest measured indoor radon in Delaware at 6.5 pCi/L, based on Airthings measurements across 34 cities.

Updated October 19, 2026

Highest city

6.5pCi/L

Bethany Beach

Delaware city average

2.1pCi/L

across 34 cities

Above action level

1/ 34

cities

Delaware Cities Ranked by Indoor Radon Levels
#	Location	Avg level	vs action level
1	Bethany Beach	6.5 pCi/L	1.6× over
✓ Below EPA action level (4 pCi/L)
2	Dover	3.9 pCi/L	1.0× under
3	Middletown	3.4 pCi/L	0.8× under
4	Clayton	3.3 pCi/L	0.8× under
5	Cheswold	3.0 pCi/L	0.7× under
6	North Star	2.8 pCi/L	0.7× under
7	Milford	2.8 pCi/L	0.7× under
8	Newark	2.8 pCi/L	0.7× under
9	Greenville	2.6 pCi/L	0.6× under
10	Hockessin	2.6 pCi/L	0.6× under
11	Rising Sun-Lebanon	2.4 pCi/L	0.6× under
12	Elsmere	2.4 pCi/L	0.6× under
13	Bellefonte	2.4 pCi/L	0.6× under
14	Pike Creek	2.4 pCi/L	0.6× under
15	Delaware City	2.3 pCi/L	0.6× under
16	Lewes	2.1 pCi/L	0.5× under
17	Glasgow	2.0 pCi/L	0.5× under
18	Harrington	1.9 pCi/L	0.5× under
19	Wilmington	1.8 pCi/L	0.5× under
20	Long Neck	1.7 pCi/L	0.4× under
21	Millsboro	1.7 pCi/L	0.4× under
22	Smyrna	1.7 pCi/L	0.4× under
23	Rehoboth Beach	1.6 pCi/L	0.4× under
24	Townsend	1.5 pCi/L	0.4× under
25	Pike Creek Valley	1.5 pCi/L	0.4× under
26	Felton	1.4 pCi/L	0.4× under
27	Newport	1.4 pCi/L	0.4× under
28	Claymont	1.3 pCi/L	0.3× under
29	Bear	1.1 pCi/L	0.3× under
30	Riverview	1.1 pCi/L	0.3× under
31	Wilmington Manor	0.9 pCi/L	0.2× under
32	Milton	0.8 pCi/L	0.2× under
33	Brookside	0.7 pCi/L	0.2× under
34	Ocean View	0.5 pCi/L	0.1× under