Franklin County, TN: EPA's radon zone, explained

EPA places Franklin 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. Franklin County sits at the 21st percentile nationally for radon potential — above 21 of every 100 rated counties.

Franklin County by the numbers

Franklin County, Tennessee is home to about 45,137 people across 554.5 square miles. That works out to roughly 81 people per square mile. By population, Franklin County is the 369th largest of every county sharing its EPA zone — the 64th percentile by population within that zone. Geologically, Franklin County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

What this actually means for a house in Franklin County

Franklin 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. Don't read Zone 3 as a pass for Franklin County — EPA's guidance to test every home makes no exception for counties predicted low.

If Franklin County tests above the action level

For a Franklin 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 Tennessee's state radon program

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

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