Onslow County, NC radon potential

EPA's own radon map rates Onslow County zone 3 - low potential, predicting a county-wide average indoor level below 2 pCi/L. Nationally, Onslow County ranks higher in radon potential than 29% of rated counties (the 29th percentile).

Where Onslow County sits nationally

Onslow County, North Carolina is home to about 212,954 people across 762.085 square miles. Averaged across its land area, Onslow County runs about 279 people per square mile. Within its own EPA zone, Onslow County is bigger by population than 88% of the counties that share it. Geologically, Onslow County is grouped into EPA Region 4 alongside 735 other counties that share its rock and soil setting.

Zone vs. an actual test

A Zone 3 county like Onslow County is predicted closer to the 0.4 pCi/L typical outdoors than to EPA's 4 pCi/L action level. Don't read Zone 3 as a pass for Onslow County — EPA's guidance to test every home makes no exception for counties predicted low.

If Onslow County tests above the action level

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 North Carolina's state radon program

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

Where Onslow County's figures come from

Onslow County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.