Ellis County, TX: EPA's radon zone, explained

Ellis County is mapped as Zone 3 - Low Potential by EPA — meaning the county-wide average indoor level is predicted below 2 pCi/L. That puts Ellis County in the 29th percentile nationally for radon potential — higher than 29% of the counties EPA has rated.

Where Ellis County sits nationally

Ellis County, Texas is home to about 232,387 people across 935.801 square miles. Population density there runs about 248 people per square mile. By population, Ellis County is the 112th largest of every county sharing its EPA zone — the 89th percentile by population within that zone. Ellis County falls in EPA Radon Region 6, one of 503 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

At Zone 3, Ellis County's predicted county average is under the national indoor average (~1.3 pCi/L) and well below EPA's 4 pCi/L action level — outdoor air nationally runs about 0.4 pCi/L for comparison. A Zone 3 label describes Ellis County's average, not any one basement or slab in it — testing is still the only way an individual homeowner actually finds out.

Testing and mitigation in Ellis County

For a Ellis 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 Texas's state radon program

For Ellis County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Ellis 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 Ellis 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.