Monmouth County, NJ: EPA's radon zone, explained

EPA places Monmouth 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 Monmouth County in the 99th percentile nationally for radon potential — higher than 99% of the counties EPA has rated.

How Monmouth County compares

Monmouth County, New Jersey is home to about 647,520 people across 468.204 square miles. That works out to roughly 1,383 people per square mile. By population, Monmouth County is the 27th largest of every county sharing its EPA zone — the 98th percentile by population within that zone. Geologically, Monmouth County is grouped into EPA Region 2 alongside 82 other counties that share its rock and soil setting.

Zone vs. an actual test

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

Testing and mitigation in Monmouth County

For a Monmouth 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 New Jersey's state radon program

For Monmouth County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Monmouth 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 Monmouth 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.