Day County, SD radon potential

Day 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 71st percentile for radon potential — Day County outranks 71% of every county EPA has rated.

How Day County compares

Day County, South Dakota is home to about 5,408 people across 1,028.49 square miles. Averaged across its land area, Day County runs about 5 people per square mile. Within its own EPA zone, Day County is bigger by population than 15% of the counties that share it. EPA's geology-based Region 8 groups Day County with 290 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Day 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. Some Day County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Next steps for a home in Day 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 South Dakota's state radon program

For Day County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Day 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 Day County's figures come from

Day County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Day County carries, the zone explainer covers what it does and doesn't tell you about any one house.