Ontario County, NY radon potential

EPA's own radon map rates Ontario County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 94th percentile for radon potential — Ontario County outranks 94% of every county EPA has rated.

Ontario County by the numbers

Ontario County, New York is home to about 113,012 people across 644.025 square miles. Averaged across its land area, Ontario County runs about 175 people per square mile. Within its own EPA zone, Ontario County is bigger by population than 84% of the counties that share it. Geologically, Ontario County is grouped into EPA Region 2 alongside 82 other counties that share its rock and soil setting.

What this actually means for a house in Ontario County

Ontario 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. Being in Zone 1 raises the odds Ontario County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

Next steps for a home in Ontario County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find New York's state radon program

For Ontario County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Ontario County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

Where Ontario County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Ontario County carries, the zone explainer covers what it does and doesn't tell you about any one house.