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

EPA's own radon map rates Marshall County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. That puts Marshall County in the 74th percentile nationally for radon potential — higher than 74% of the counties EPA has rated.

How Marshall County compares

Marshall County, Minnesota is home to about 8,771 people across 1,775.06 square miles. Averaged across its land area, Marshall County runs about 5 people per square mile. By population, Marshall County is the 802nd largest of every county sharing its EPA zone — the 25th percentile by population within that zone. Marshall County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Marshall County

Marshall 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. Some Marshall County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

If Marshall County tests above the action level

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

Where Marshall County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Marshall County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.