What EPA's radon map says about Franklin County

EPA places Franklin 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 that's the 48th percentile for radon potential — Franklin County outranks 48% of every county EPA has rated.

Franklin County by the numbers

About 23,136 people live in Franklin County, Indiana, spread over 384.426 square miles. Averaged across its land area, Franklin County runs about 60 people per square mile. Among counties sharing Franklin County's EPA zone, it outranks 44% of them by population. Franklin County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

EPA's Zone 2 rating for Franklin County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. A county-wide moderate average, like Franklin County's, can still hide a specific house well above or below it — testing is what actually answers the question.

If Franklin County tests above the action level

Mitigation cost doesn't depend on Franklin 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 Indiana's state radon program

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

More on how this number was built

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