Local radon context
Radon Levels by County and State
Compare EPA zone context and source-backed local records. County data is context, not a substitute for testing the home you live in.
Already have a number from a radon report?
Interpret my test resultWhat county context can tell you
EPA zone
A county-level potential category, useful for context but never a home measurement.
Official local records
Some county pages include state or public-health tables with period and source limits shown.
What it cannot tell you
It cannot predict the radon level in one basement, slab, or crawl-space home.
Directory guide
Use local evidence without mistaking it for your result
Start with your state, then open a listed county source. Each page makes the geography, source period, and statistical limit visible before asking you to act.
Browse by state
Open the state hub first when you need county-level EPA zone or public source context.
Open state directory →Read the source base
See which public source is used and why a county summary has limits.
Open data sources →Already have a report?
Use the result interpreter for test-type-aware next steps rather than comparing your number to a county average.
Interpret my result →No report yet?
Start with a correctly placed test. A zone map is never a substitute for it.
Read testing guide →Radon gas testing in Ulster County, NY
Use the dedicated local guide when the question is how to place the test, preserve closed-house conditions, and act on the result—not just what the county level data says.
Open the Ulster County testing guide →Radon testing in Powhatan County, VA
Placement, closed-house conditions, local evidence, and the decision after the result.
Open Powhatan testing →Radon testing in Broomfield County, CO
A test-first path for searchers who are otherwise sent straight to mitigation pages.
Open Broomfield testing →Commercial radon testing in Los Angeles County
Build a compliant measurement scope for multifamily, mixed-use, school, office, retail, or other non-residential property before asking for a mitigation bid.
Open commercial testing protocol →Choose your next step
Start from the exact job, not another generic radon article.
Pick the situation that matches your home. Each route keeps the reading, deal side, or foundation clue attached so the next page answers the search instead of resetting the user.
Failed inspection
I need a repair or seller credit number
Open the local credit path with a 4.0+ buyer scenario already selected.
Open negotiation route4.0+ pCi/L
I have a high result and need the cost path
Go straight to the county estimate, quote context, and contractor checklist.
Open cost route2.0-3.9 pCi/L
I need to know if this number is bad
Use the level explanation first, then decide whether to retest, monitor, or price mitigation.
Open level routeNo test yet
I need the first valid result
Start with kit placement, timing, closed-house conditions, and result interpretation.
Open testing routeOfficial County Data
Every listed county page is tied to an official radon source
Coverage currently spans 119 listed county pages. Measured counties use official state tables or CDC Tracking summaries; map-classified counties use official radon-potential categories when a county pCi/L table is not published.
100%
official support
Measured counties
112
State tables
62
Map classified
7
More county detail
0
Open Official-Data States First
Route from the national threshold to state-specific radon data
Some states publish county measurements, while others are best read through CDC Tracking or official radon-potential maps. Start with the states below when you need county pages with clearer public data behind the recommendation.
State measurements
Iowa HHS publishes county median radon values. Osceola County, IA shows an 11.4 pCi/L median, so its page should be opened before treating Iowa as only a zone-map question.
Highest measured examples
North Carolina DHHS maps the highest measured radon level by county. Rutherford County, NC shows 681 pCi/L as a high-end county signal, not a county average.
CDC and map coverage
CDC summaries and official state/federal radon-potential maps still help when a state does not publish a county measurement table. Use them as context, then let a home test decide.
National Data Guide
Start with the national action threshold, then open states with the strongest county evidence.
This page connects the plain 2.0, 4.0, and 8.0 pCi/L answer to state hubs where county evidence is strongest: 119 of 119 surfaced county pages have official evidence, with 112 measured county summaries and 7 official map-classification summaries.
112
measured counties
Official source base
Official source base: 62 county summaries come from state-specific or federal measurement tables, 50 use CDC Tracking, 7 use official state or federal map classifications, and 0 need more county-specific detail. That helps users tell the difference between a county with reported test data and a broader map guide.
How to use it
Most surfaced county pages now have official evidence behind them, so users can start with source-backed pages instead of a generic national answer.
Where county detail is lighter
Some counties still depend on broader federal summaries or state pages without county pCi/L metrics. In those cases, use the county page as context and let a fresh home test control the decision.
Open these state hubs first
States with the strongest county evidence
Ranked by official coverage, measured county pages, elevated/high county count, and state measurement strength.
VA
12 state measurement summaries
12/12 counties with official support
12 measured, 0 map-classified
9 elevated/high, 5 high
VA is a strong starting point because it has 5 counties with high measured radon signals and 12 state measurement summaries.
PA
7 state measurement, 3 CDC
10/10 counties with official support
10 measured, 0 map-classified
9 elevated/high, 9 high
PA is a strong starting point because it has 9 counties with high measured radon signals and 7 state measurement summaries.
NY
8 state measurement summaries
8/8 counties with official support
8 measured, 0 map-classified
5 elevated/high, 4 high
NY is a strong starting point because it has 4 counties with high measured radon signals and 8 state measurement summaries.
IL
6 state measurement summaries
6/6 counties with official support
6 measured, 0 map-classified
6 elevated/high, 5 high
IL is a strong starting point because it has 5 counties with high measured radon signals and 6 state measurement summaries.
CO
5 state measurement summaries
5/5 counties with official support
5 measured, 0 map-classified
5 elevated/high, 3 high
CO is a strong starting point because it has 3 counties with high measured radon signals and 5 state measurement summaries.
TN
5 state measurement summaries
5/5 counties with official support
5 measured, 0 map-classified
5 elevated/high, 3 high
TN is a strong starting point because it has 3 counties with high measured radon signals and 5 state measurement summaries.
OH
7 CDC summaries
7/7 counties with official support
7 measured, 0 map-classified
7 elevated/high, 6 high
OH is a strong starting point because it has 6 counties with high measured radon signals and 0 state measurement summaries.
IA
3 state measurement summaries
3/3 counties with official support
3 measured, 0 map-classified
3 elevated/high, 1 high
IA is a strong starting point because it has 1 counties with high measured radon signals and 3 state measurement summaries.
Direct Answer
What radon level should homeowners act on?
In US guidance, 4.0 pCi/L or higher is the main action threshold for fixing a home. Results from 2.0 to 3.9 pCi/L still deserve attention because radon risk is not zero below 4.0; retest, track long-term, or consider reduction depending on the home and situation.
| Evidence | Value |
|---|---|
| Under 2.0 pCi/L | Lower concern; keep periodic testing |
| 2.0 to 3.9 pCi/L | Retest, track, or consider reduction |
| 4.0+ pCi/L | EPA action threshold for fixing the home |
| 8.0+ pCi/L | High reading; prioritize mitigation planning |
Have a report
Interpret the result
Use the national threshold and your test type, not a county average, for the next decision.
Need a test
Test the actual home
A correctly placed home test is the only way to know the level where you live.
Trust & Sources
Read the Methodology
See how public EPA, state, and public-health data are distinguished from a property-level result.
EPA Zone Context
EPA zones are map context, not your home result
EPA radon zones estimate county-level potential. They are useful for deciding how seriously to treat local risk, but the reading inside one basement, slab home, or crawl-space home can be higher or lower than the county prediction.
Zone 1 counties
Highest predicted average potential. Testing and mitigation planning deserve early attention.
Zone 2 counties
Moderate predicted average potential. Borderline readings should not be dismissed.
Zone 3 counties
Lower predicted average potential. Direct testing is still the deciding evidence.
State and County Maps
Browse radon levels by state
119 county pages currently available in the state map directory.
Sources and limits
This page uses EPA radon action-level guidance and EPA zone data for public-risk context. It is not medical advice, legal advice, or a substitute for a valid home radon test. If you already have a result, your own measured level matters more than the county zone.
Editorial and Data Transparency
- Author
- RadonVerdict Data Team (Public Data and Cost Modeling)
- Content Review
- Source-level dates shown below
- Data Retrieved At
- Source-level dates below
Primary Sources
- EPA Map of Radon Zones (retrieved 2026-02-21)
- EPA A Citizen's Guide to Radon (retrieved 2026-05-05)
- CDC Environmental Public Health Tracking - Radon Testing (retrieved 2026-05-05)
- Angi Radon Mitigation Cost Guide (retrieved 2026-02-21)