Ontonagon County, MI radon potential
EPA places Ontonagon County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Ontonagon County ranks higher in radon potential than 3% of rated counties (the 3rd percentile).
How Ontonagon County compares
Ontonagon County, Michigan is home to about 5,824 people across 1,310.978 square miles. Averaged across its land area, Ontonagon County runs about 4 people per square mile. Within its own EPA zone, Ontonagon County is bigger by population than 10% of the counties that share it. Geologically, Ontonagon County is grouped into EPA Region 5 alongside 523 other counties that share its rock and soil setting.
Zone vs. an actual test
Ontonagon County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. Even at Zone 3, Ontonagon County homes are not guaranteed a low reading — zone is a county-wide average, and EPA recommends testing every home regardless of zone.
If Ontonagon County tests above the action level
A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.
Find Michigan's state radon program
For Ontonagon County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Ontonagon 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 Ontonagon 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 Ontonagon County carries, the zone explainer covers what it does and doesn't tell you about any one house.