Sangamon County, IL: EPA's radon zone, explained

EPA places Sangamon County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Sangamon County sits at the 97th percentile nationally for radon potential — above 97 of every 100 rated counties.

Sangamon County by the numbers

Sangamon County, Illinois is home to about 194,345 people across 868.23 square miles. That works out to roughly 224 people per square mile. By population, Sangamon County is the 100th largest of every county sharing its EPA zone — the 91st percentile by population within that zone. Sangamon County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Sangamon County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. Being in Zone 1 raises the odds Sangamon County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

Testing and mitigation in Sangamon County

For a Sangamon 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 Illinois's state radon program

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