Radon in Connecticut: radon map by county
EPA's Map of Radon Zones puts 3 of Connecticut's 9 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 0 in Zone 2 and 0 in Zone 3; 6 have no single zone.
Radon by county in Connecticut
Connecticut abolished county government in 1960 and its nine planning regions have replaced the eight counties in federal statistics since 2022. EPA's 1993 zones are by the old counties, so each planning region below shows the zone of the former county where all its towns lie, or “mixed” when its towns came from counties in different zones. An address lookup places the address in its former county.
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Capitol Planning Region | Mixed (Zones 2 and 3) | n/a | n/a | n/a |
| Greater Bridgeport Planning Region | Zone 1 | n/a | n/a | n/a |
| Lower Connecticut River Valley Planning Region | Zone 1 | n/a | n/a | n/a |
| Naugatuck Valley Planning Region | Mixed (Zones 1 and 2 and 3) | n/a | n/a | n/a |
| Northeastern Connecticut Planning Region | Mixed (Zones 1 and 2) | n/a | n/a | n/a |
| Northwest Hills Planning Region | Mixed (Zones 2 and 3) | n/a | n/a | n/a |
| South Central Connecticut Planning Region | Zone 1 | n/a | n/a | n/a |
| Southeastern Connecticut Planning Region | Mixed (Zones 1 and 2) | n/a | n/a | n/a |
| Western Connecticut Planning Region | Mixed (Zones 1 and 2) | n/a | n/a | n/a |
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 Connecticut: questions
What radon zone is Connecticut?
EPA's 1993 map does not give states one zone; it zones each county. In Connecticut, 3 counties are Zone 1, 0 Zone 2 and 0 Zone 3. Connecticut now reports planning regions instead of counties; each region page lists the zones of the former counties its towns were in. EPA says the map "should not be used to determine if individual homes need to be tested".
Should I test for radon in Connecticut?
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 Connecticut
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 Connecticut · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.