St. Louis city, MO: EPA's radon zone, explained

St. Louis city is mapped as Zone 2 - Moderate Potential by EPA — meaning the county-wide average indoor level is predicted between 2 and 4 pCi/L. That puts St. Louis city in the 63rd percentile nationally for radon potential — higher than 63% of the counties EPA has rated.

Where St. Louis city sits nationally

St. Louis city, Missouri is home to about 279,695 people across 61.717 square miles. Averaged across its land area, St. Louis city runs about 4,532 people per square mile. By population, St. Louis city is the 85th largest of every county sharing its EPA zone — the 92nd percentile by population within that zone. Geologically, St. Louis city is grouped into EPA Region 7 alongside 411 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

EPA's Zone 2 rating for St. Louis city sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. Middle-of-the-pack doesn't mean risk-free for any one St. Louis city address — a moderate county average still leaves individual homes to test either side of it.

Testing and mitigation in St. Louis city

For a St. Louis city 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 Missouri's state radon program

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

Where St. Louis city's figures come from

The methodology guide shows exactly which EPA and Census sources feed St. Louis city's numbers. Whatever zone St. Louis city carries, the zone explainer covers what it does and doesn't tell you about any one house.