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

EPA places Noble County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. That puts Noble County in the 90th percentile nationally for radon potential — higher than 90% of the counties EPA has rated.

Where Noble County sits nationally

Noble County, Indiana is home to about 47,811 people across 410.843 square miles. Population density there runs about 116 people per square mile. By population, Noble County is the 327th largest of every county sharing its EPA zone — the 69th percentile by population within that zone. EPA's geology-based Region 5 groups Noble County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Noble County

Noble County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. 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 Noble County specifically.

Testing and mitigation in Noble County

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

Where Noble County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Noble County carries, the zone explainer covers what it does and doesn't tell you about any one house.