Radon Levels by ZIP Code

Your ZIP code can tell you your county's radon potential, not your home's radon level. EPA's Map of Radon Zones puts 1,074 U.S. counties in Zone 1, where the predicted average indoor screening level is above 4 pCi/L, 1,034 in Zone 2 (2 to 4 pCi/L) and 1,036 in Zone 3 (below 2 pCi/L), by our count of EPA's file.

Read this with your result.

EPA's zone map is from 1993 and county-level, and EPA says it should not be used to determine if individual homes need to be tested. Homes with high radon have been found in all three zones.
In EPA's own validation, 72% of county screening averages matched the assigned zone; the rest were one zone off (EPA National Summary).
ZIP codes are not counties. In the Census Bureau relationship file, 10,186 of 33,791 ZIP areas cross county lines, and 2,052 include counties in different zones (our count). We show the zone of the county covering most of the ZIP's land, plus the others.
State test data comes from voluntary tests. People who suspect radon test more often, and Pennsylvania's data cannot separate post-mitigation retests (the DEP field is not collected).
A ZIP or county figure says nothing reliable about one house. Only a test of your home tells you your level (EPA).
No medical advice: see EPA and your state radon office.

What the EPA radon zones mean

EPA built the map in 1993 from five inputs: indoor radon measurements, geology, aerial radioactivity, soil permeability and foundation types. It assigned each county the zone of the geologic province covering most of it, to help governments target outreach and radon-resistant building codes. EPA says the map should not be used to determine if individual homes need to be tested, and that homes with elevated radon have been found in all three zones.

Where we have local test results

Pennsylvania: ZIP-level results from the Department of Environmental Protection's public test data set. Across 2,644,039 basement tests from July 1985 to July 2026, 37.3% read 4 pCi/L or higher, by our count. We show a ZIP only when it has at least 30 basement tests: 1,452 ZIPs qualify.
Ohio: county results from the Ohio Department of Health dashboard. 34.4% of 525,229 tests read 4 pCi/L or higher, test-weighted across 88 counties, by our count.
Coming next: Colorado, Minnesota and Iowa county data from their state programs.

Worked lookup

ZIP	County (EPA zone)	State data	Reading
16801 State College, PA	Centre County (Zone 1)	PA DEP: 14,691 basement tests, 55.0% at or above 4 pCi/L	High potential; test
17402 York, PA	York County (Zone 1)	PA DEP: 8,558 basement tests, 59.8% at or above 4 pCi/L	High potential; test
19148 Philadelphia, PA	Philadelphia County (Zone 2)	PA DEP: 7,400 basement tests, 4.2% at or above 4 pCi/L	Lower share, but still test

The three Pennsylvania ZIPs show why local data matters. State College's 16801 and York's 17402 had 55.0% and 59.8% of basement tests at or above 4 pCi/L, while South Philadelphia's 19148 had 4.2% (PA DEP data, our count). A county zone alone would not show that spread.

How to read your result

Zone 1: your county's predicted average screening level is above 4 pCi/L, EPA's action level. Test soon. In Pennsylvania's Zone 1 counties, the DEP data shows many ZIPs with half or more of basement tests at or above 4 pCi/L.

Zone 2: a predicted average of 2 to 4 pCi/L, the range where EPA says to consider fixing. Plenty of homes in Zone 2 counties test above 4 pCi/L.

Zone 3: below 2 pCi/L predicted. EPA still recommends testing, because elevated homes turn up in every zone.

State data shown: treat the share of tests at or above 4 pCi/L as a rough guide to how common high readings are nearby, not as your number.

What to do with your result

Step 1: Test your home, whatever the zone. Short-term kits cost $10 to $30 and professional tests $125 to $400 (HomeGuide, Feb 2026), and many state radon offices offer free or discounted kits.
Step 2: If the result is 4 pCi/L or higher, fix it; between 2 and 4 pCi/L, consider fixing (EPA Citizen's Guide, 2016).
Step 3: Price a system with the radon mitigation cost calculator. Most sub-slab systems run $1,200 to $2,000 installed (HomeGuide).
Step 4: Hire a mitigator holding your state's credential. Pennsylvania requires DEP certification (25 Pa. Code Chapter 240) and Ohio requires an ODH license (OAC 3701-69).
Step 5: Retest after installation (EPA Consumer's Guide).

State guides:

Questions

Is my ZIP code safe from radon?

No ZIP is safe by default. EPA reports elevated homes in every zone. Only a test of your home answers it.

Why is my neighbor's level different from mine?

Soil under each slab, foundation cracks, and how the house holds air all vary house to house. That is why EPA tells every home to test.

Where do I get a free test kit?

Ask your state radon office; many offer free or low-cost kits (HomeGuide notes some states provide free short-term kits).

How often is this data updated?

We rebuild when EPA, the Census Bureau or a state publishes a new file. Pennsylvania data was retrieved October 16, 2026, and runs through July 6, 2026.