Middlesex County, MA Radon Zone Data

Middlesex County, MA radon potential

Middlesex County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally that's the 100th percentile for radon potential — Middlesex County outranks 100% of every county EPA has rated.

Where Middlesex County sits nationally

Middlesex County, Massachusetts is home to about 1,668,956 people across 817.905 square miles. That works out to roughly 2,041 people per square mile. Within its own EPA zone, Middlesex County is bigger by population than 100% of the counties that share it. Geologically, Middlesex County is grouped into EPA Region 1 alongside 58 other counties that share its rock and soil setting.

What this actually means for a house in Middlesex County

Middlesex 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. 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 Middlesex County specifically.

Testing and mitigation in Middlesex County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Massachusetts's state radon program

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

Where Middlesex County's figures come from

Middlesex County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.