Allen County, IN: EPA's radon zone, explained

Allen County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Rank it against the rest of the country and Allen County lands in the 98th percentile for radon potential.

Allen County by the numbers

Allen County, Indiana is home to about 399,295 people across 657.146 square miles. Population density there runs about 608 people per square mile. By population, Allen County is the 55th largest of every county sharing its EPA zone — the 95th percentile by population within that zone. Geologically, Allen County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Allen County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. EPA's guidance doesn't change because of a Zone 1 label: test the house. What changes is the reason to not put it off in Allen County specifically.

Next steps for a home in Allen County

For a Allen 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 Indiana's state radon program

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

Allen County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.