Washington County, MN: EPA's radon zone, explained

EPA's own radon map rates Washington County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 98th percentile for radon potential — Washington County outranks 98% of every county EPA has rated.

Where Washington County sits nationally

Washington County, Minnesota is home to about 283,960 people across 384.762 square miles. That works out to roughly 738 people per square mile. By population, Washington County is the 79th largest of every county sharing its EPA zone — the 93rd percentile by population within that zone. Geologically, Washington 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 Washington County

Where the national indoor average runs about 1.3 pCi/L, Washington County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. 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 Washington County specifically.

Testing and mitigation in Washington County

For a Washington 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 Minnesota's state radon program

For Washington County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Washington 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 Washington County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Washington County's numbers. Whatever zone Washington County carries, the zone explainer covers what it does and doesn't tell you about any one house.