Brown County, SD: EPA's radon zone, explained

Brown County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Brown County sits at the 87th percentile nationally for radon potential — above 87 of every 100 rated counties.

How Brown County compares

Brown County, South Dakota is home to about 37,495 people across 1,713.03 square miles. Averaged across its land area, Brown County runs about 22 people per square mile. By population, Brown County is the 402nd largest of every county sharing its EPA zone — the 62nd percentile by population within that zone. EPA's geology-based Region 8 groups Brown County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Brown County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. 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 Brown County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Brown County

For a Brown 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 South Dakota's state radon program

For Brown County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Brown 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 Brown 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. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.