Radon in Maryland
About 1 in 4 homes tested in Maryland were at or above the EPA action level of 4 pCi/L.
- Below 2 pCi/L: 56%
- 2 to 4 pCi/L: 20%
- 4 pCi/L or more: 24%
The EPA puts 8 of Maryland's 24 counties in Zone 1, its highest radon category, 9 in Zone 2 and 7 in Zone 3.
Every county in Maryland
Sorted by the share of homes tested at or above 4 pCi/L. Select a county for local details and costs.
| County | Homes tested | At or above 4 | Median | EPA zone |
|---|---|---|---|---|
| Washington County | 56% | 5.2 pCi/L | 1 | |
| Kent County | 53% | 4.4 pCi/L | 3 | |
| Carroll County | 42% | 2.8 pCi/L | 1 | |
| Garrett County | 37% | 3.0 pCi/L | 2 | |
| Allegany County | 36% | 2.7 pCi/L | 2 | |
| Howard County | 31% | 2.0 pCi/L | 1 | |
| Calvert County | 30% | 2.0 pCi/L | 1 | |
| Frederick County | 28% | 1.5 pCi/L | 1 | |
| Cecil County | 25% | 1.9 pCi/L | 2 | |
| Charles County | 24% | 1.8 pCi/L | 2 | |
| Harford County | 23% | 1.7 pCi/L | 1 | |
| St. Mary's County | 21% | 1.8 pCi/L | 2 | |
| Baltimore County | 19% | 1.4 pCi/L | 1 | |
| Prince George's County | 19% | 1.4 pCi/L | 2 | |
| Montgomery County | 18% | 1.3 pCi/L | 1 | |
| Anne Arundel County | 17% | 1.4 pCi/L | 2 | |
| Queen Anne's County | 17% | 1.3 pCi/L | 3 | |
| Dorchester County | 5 tests | – | – | 3 |
| Baltimore city | 8% | 0.8 pCi/L | 2 | |
| Talbot County | 8% | 1.1 pCi/L | 3 | |
| Caroline County | 10 tests | – | – | 3 |
| Somerset County | 2 tests | – | – | 2 |
| Wicomico County | 18 tests | – | – | 3 |
| Worcester County | 7 tests | – | – | 3 |
"–" means fewer than 20 tests or no lab data, too few for a reliable figure.
Sources
- EPA Map of Radon Zones (public domain).
- CDC Environmental Public Health Tracking Network, radon tests from labs, 2008–2017. Pre-mitigation tests only.
Last updated October 2026. How we calculate these numbers.