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

EPA's own radon map rates Harrison County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Harrison County lands in the 88th percentile for radon potential.

Where Harrison County sits nationally

Harrison County, Indiana is home to about 39,978 people across 484.081 square miles. Population density there runs about 83 people per square mile. By population, Harrison County is the 378th largest of every county sharing its EPA zone — the 65th percentile by population within that zone. Harrison County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

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 — Harrison 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 Harrison County specifically.

Next steps for a home in Harrison County

For a Harrison 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 Harrison County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Harrison County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Harrison County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Harrison County's numbers. Whatever zone Harrison County carries, the zone explainer covers what it does and doesn't tell you about any one house.