St. Joseph County, IN Radon Zone Data

What EPA's radon map says about St. Joseph County

EPA places St. Joseph 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 St. Joseph County in the 97th percentile nationally for radon potential — higher than 97% of the counties EPA has rated.

Where St. Joseph County sits nationally

About 273,744 people live in St. Joseph County, Indiana, spread over 457.781 square miles. Averaged across its land area, St. Joseph County runs about 598 people per square mile. Among counties sharing St. Joseph County's EPA zone, it outranks 92% of them by population. Geologically, St. Joseph County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.

What this actually means for a house in St. Joseph County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — St. Joseph 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 St. Joseph County specifically.

Next steps for a home in St. Joseph County

Mitigation cost doesn't depend on St. Joseph 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

St. Joseph County's test kit answers today; a Airthings radon monitor keeps answering for St. Joseph 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

St. Joseph County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone St. Joseph County carries, the zone explainer covers what it does and doesn't tell you about any one house.