What EPA's radon map says about Grant County

EPA places Grant 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. Nationally that's the 90th percentile for radon potential — Grant County outranks 90% of every county EPA has rated.

Where Grant County sits nationally

About 52,330 people live in Grant County, Wisconsin, spread over 1,147.604 square miles. Population density there runs about 46 people per square mile. Among counties sharing Grant County's EPA zone, it outranks 71% of them by population. EPA's geology-based Region 5 groups Grant County with 523 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Grant County

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Grant 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 Grant County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Grant County

Mitigation cost doesn't depend on Grant County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Wisconsin's state radon program

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

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