Marion County, OR radon potential

EPA places Marion County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Marion County ranks higher in radon potential than 31% of rated counties (the 31st percentile).

Where Marion County sits nationally

Marion County, Oregon is home to about 352,867 people across 1,180.84 square miles. Averaged across its land area, Marion County runs about 299 people per square mile. Within its own EPA zone, Marion County is bigger by population than 93% of the counties that share it. Geologically, Marion County is grouped into EPA Region 10 alongside 141 other counties that share its rock and soil setting.

Zone vs. an actual test

Marion County's Zone 3 prediction undercuts the roughly 1.3 pCi/L most US homes average, nowhere near EPA's 4 pCi/L threshold for recommending mitigation. Even at Zone 3, Marion 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 Marion 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 Oregon's state radon program

For Marion County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Marion 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 Marion County's figures come from

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