St. Joseph County, MI: EPA's radon zone, explained

EPA's own radon map rates St. Joseph County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts St. Joseph County in the 91st percentile nationally for radon potential — higher than 91% of the counties EPA has rated.

How St. Joseph County compares

St. Joseph County, Michigan is home to about 61,171 people across 500.639 square miles. That works out to roughly 122 people per square mile. By population, St. Joseph County is the 271st largest of every county sharing its EPA zone — the 75th percentile by population within that zone. Geologically, St. Joseph 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

St. Joseph County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. 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

For a St. Joseph 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 Michigan's state radon program

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

Where St. Joseph 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. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.