Monterey County, CA radon potential
EPA places Monterey County in Zone 2 - Moderate Potential — a predicted county-wide average indoor radon level between 2 and 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Monterey County ranks higher in radon potential than 64% of rated counties (the 64th percentile).
Where Monterey County sits nationally
Monterey County, California is home to about 436,251 people across 3,281.718 square miles. Population density there runs about 133 people per square mile. Within its own EPA zone, Monterey County is bigger by population than 95% of the counties that share it. Monterey County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.
Why the zone isn't the answer by itself
Monterey County's predicted average falls between EPA's 4 pCi/L action level and the national indoor average of about 1.3 pCi/L (outdoor air runs roughly 0.4 pCi/L). Monterey County's Zone 2 rating sits in the middle nationally; EPA's guidance is unchanged by that — test every home regardless of its zone.
Testing and mitigation in Monterey 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 California's state radon program
For Monterey County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Monterey County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.
Where Monterey County's figures come from
Monterey County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.