Is Tompkins County, NY a radon risk area?
Tompkins County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Tompkins County in the 94th percentile nationally for radon potential — higher than 94% of the counties EPA has rated.
Tompkins County by the numbers
About 105,602 people live in Tompkins County, New York, spread over 474.65 square miles. That works out to roughly 222 people per square mile. Rank 186 by population within its EPA zone puts Tompkins County at the 83rd percentile among zone peers. EPA's geology-based Region 2 groups Tompkins County with 82 other counties nationally sharing its underlying rock and soil profile.
What this actually means for a house in Tompkins County
Tompkins County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Tompkins County will test well under the action level, and EPA's guidance is to test regardless of zone.
Next steps for a home in Tompkins County
Nothing about Tompkins County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.
Find New York's state radon program
Tompkins County's test kit answers today; a Airthings radon monitor keeps answering for Tompkins County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.
More on how this number was built
The methodology guide shows exactly which EPA and Census sources feed Tompkins County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.