Yolo County, CA: EPA's radon zone, explained

Yolo County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. Rank it against the rest of the country and Yolo County lands in the 29th percentile for radon potential.

Yolo County by the numbers

Yolo County, California is home to about 225,251 people across 1,012.988 square miles. Population density there runs about 222 people per square mile. By population, Yolo County is the 114th largest of every county sharing its EPA zone — the 89th percentile by population within that zone. Yolo County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Yolo County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. Even at Zone 3, Yolo County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.

Testing and mitigation in Yolo County

For a Yolo County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find California's state radon program

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

Where Yolo County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Yolo County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.