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 26 cities.
Updated August 16, 2026
Highest city
6.5pCi/L
Bethany Beach
Delaware city average
2.2pCi/L
across 26 cities
Above action level
1/ 26
cities
| # | Location | Avg level | Monitors | vs action level |
|---|---|---|---|---|
| 1 | Bethany Beach | 6.5 pCi/L | 6 | 1.6× over |
| ✓ Below EPA action level (4 pCi/L) | ||||
| 2 | Dover | 3.9 pCi/L | 7 | 1.0× under |
| 3 | Clayton | 3.6 pCi/L | 6 | 0.9× under |
| 4 | Middletown | 3.4 pCi/L | 101 | 0.8× under |
| 5 | Cheswold | 3.0 pCi/L | 10 | 0.8× under |
| 6 | North Star | 2.8 pCi/L | 18 | 0.7× under |
| 7 | Milford | 2.8 pCi/L | 7 | 0.7× under |
| 8 | Greenville | 2.6 pCi/L | 28 | 0.7× under |
| 9 | Hockessin | 2.6 pCi/L | 27 | 0.6× under |
| 10 | Delaware City | 2.4 pCi/L | 24 | 0.6× under |
| 11 | Newark | 2.4 pCi/L | 36 | 0.6× under |
| 12 | Bellefonte | 2.1 pCi/L | 39 | 0.5× under |
| 13 | Lewes | 2.1 pCi/L | 61 | 0.5× under |
| 14 | Glasgow | 1.9 pCi/L | 42 | 0.5× under |
| 15 | Wilmington | 1.8 pCi/L | 20 | 0.4× under |
| 16 | Smyrna | 1.7 pCi/L | 8 | 0.4× under |
| 17 | Rehoboth Beach | 1.6 pCi/L | 8 | 0.4× under |
| 18 | Pike Creek Valley | 1.5 pCi/L | 15 | 0.4× under |
| 19 | Townsend | 1.5 pCi/L | 19 | 0.4× under |
| 20 | Newport | 1.4 pCi/L | 6 | 0.4× under |
| 21 | Claymont | 1.3 pCi/L | 15 | 0.3× under |
| 22 | Bear | 1.1 pCi/L | 10 | 0.3× under |
| 23 | Wilmington Manor | 0.9 pCi/L | 7 | 0.2× under |
| 24 | Milton | 0.8 pCi/L | 7 | 0.2× under |
| 25 | Brookside | 0.6 pCi/L | 8 | 0.2× under |
| 26 | Ocean View | 0.5 pCi/L | 8 | 0.1× under |