What EPA's radon map says about Knox County

EPA places Knox County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Knox County sits at the 99th percentile nationally for radon potential — above 99 of every 100 rated counties.

How Knox County compares

About 506,748 people live in Knox County, Tennessee, spread over 508.325 square miles. Population density there runs about 997 people per square mile. Among counties sharing Knox County's EPA zone, it outranks 96% of them by population. EPA's geology-based Region 4 groups Knox County with 735 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Knox County

Where the national indoor average runs about 1.3 pCi/L, Knox County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. Being in Zone 1 raises the odds Knox 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 Knox County

Mitigation cost doesn't depend on Knox County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Tennessee's state radon program

Knox County's test kit answers today; a Airthings radon monitor keeps answering for Knox County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Knox County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.