Radon in Maine: radon map by county
EPA's Map of Radon Zones puts 12 of Maine's 16 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 4 in Zone 2 and 0 in Zone 3. Of 8,788 building tests that radon laboratories reported for 2008 to 2017, 38.5% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 17 of 42 states with 1,000+ tests). The highest county share is York County (48.4% of 1,070 tests).
Radon by county in Maine
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Androscoggin County | Zone 1 | 1,294 | 2.8 | 36.9% |
| Aroostook County | Zone 1 | 370 | 3.5 | 45.1% |
| Cumberland County | Zone 1 | 3,173 | 3.2 | 43.5% |
| Franklin County | Zone 1 | 118 | 1.8 | 29.1% |
| Hancock County | Zone 1 | 214 | 2.6 | 39.1% |
| Kennebec County | Zone 1 | 566 | 2.1 | 30.3% |
| Knox County | Zone 2 | 206 | 2.3 | 29.6% |
| Lincoln County | Zone 1 | 192 | 2.5 | 35.8% |
| Oxford County | Zone 1 | 344 | 3.3 | 43.1% |
| Penobscot County | Zone 1 | 749 | 0.8 | 16.4% |
| Piscataquis County | Zone 1 | 33 | 3.5 | 47.7% |
| Sagadahoc County | Zone 2 | 224 | 2.1 | 30% |
| Somerset County | Zone 1 | 58 | 1.5 | 18.8% |
| Waldo County | Zone 2 | 142 | 2.3 | 32.1% |
| Washington County | Zone 2 | 35 | 1.6 | 29.6% |
| York County | Zone 1 | 1,070 | 3.7 | 48.4% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
Radon in Maine: questions
What radon zone is Maine?
EPA's 1993 map does not give states one zone; it zones each county. In Maine, 12 counties are Zone 1, 4 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Maine counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): York County 48.4% (median 3.7 pCi/L, 1,070 tests); Piscataquis County 47.7% (median 3.5 pCi/L, 33 tests); Aroostook County 45.1% (median 3.5 pCi/L, 370 tests); Cumberland County 43.5% (median 3.2 pCi/L, 3,173 tests); Oxford County 43.1% (median 3.3 pCi/L, 344 tests).
How common is high radon in Maine?
38.5% of the 8,788 tests in the laboratory data for Maine (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Should I test for radon in Maine?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Maine
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Maine · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.