Franklin County, MO radon potential

Franklin County is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. Nationally that's the 60th percentile for radon potential — Franklin County outranks 60% of every county EPA has rated.

Franklin County by the numbers

Franklin County, Missouri is home to about 107,256 people across 922.491 square miles. Averaged across its land area, Franklin County runs about 116 people per square mile. Within its own EPA zone, Franklin County is bigger by population than 82% of the counties that share it. EPA's geology-based Region 7 groups Franklin County with 411 other counties nationally sharing its underlying rock and soil profile.

Why the zone isn't the answer by itself

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Franklin County's Zone 2 prediction. Nothing about a Zone 2 label lowers the case for testing in Franklin County — EPA recommends it in every zone, moderate included.

Next steps for a home in Franklin 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 Missouri'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. Code RADONZONE-10OFF takes 10% off at checkout.

Where Franklin County's figures come from

Franklin County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.