Is Washtenaw County, MI a radon risk area?

EPA places Washtenaw 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 Washtenaw County in the 98th percentile nationally for radon potential — higher than 98% of the counties EPA has rated.

Washtenaw County by the numbers

About 373,875 people live in Washtenaw County, Michigan, spread over 706.015 square miles. Population density there runs about 530 people per square mile. Rank 64 by population within its EPA zone puts Washtenaw County at the 94th percentile among zone peers. Geologically, Washtenaw 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

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Washtenaw County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Washtenaw County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Washtenaw County

Nothing about Washtenaw County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Michigan's state radon program

Washtenaw County's test kit answers today; a Airthings radon monitor keeps answering for Washtenaw 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

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