Montana Radon Map by County, EPA Zones & Basement Testing
Check the listed EPA radon zone pages across Montana. Start with a listed county if you want to know what a basement result means at 2.0 vs 4.0+ pCi/L before you price mitigation.
High Risk
Moderate
Low Risk
Official Evidence in Montana
10 of 10 listed counties have official evidence
Open a county page to see the processed verdict: source confidence, local burden, state percentile, and the next step for no reading, 2.0-3.9, or 4.0+ pCi/L.
100%
covered
Measured
10
State source
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CDC source
10
Needs source detail
0
Measured Risk Leaders in Montana
County rankings from actual reported radon tests
These lists rank the visible Montana county pages by measured radon signals, not by the EPA zone label alone. Use them to spot where the state hub has a real data story before opening individual county pages.
10
measured counties
State-level verdict
This hub has measured high-burden counties, so the first click should be evidence-led.
The state hub is now doing a decision job: it separates first-click counties, retest counties, and lower-signal counties from 10 visible county measurement rows. 9 counties cross the high measured-burden band, so those pages should answer testing and 4.0+ action questions most directly.
First-click counties
Open Lincoln County first when you need the strongest local answer. It is tagged Test-now from 51.4% 4.0+ - 19.3 pCi/L primary - 51 tests. 10 visible measured counties are elevated or high enough to review before lower-signal counties.
Buyer/seller lane
Buyer/seller lane: start with the elevated or high counties, require a fresh lowest-level test, and turn any 4.0+ property result into quote or credit math. The hub has 10 CDC-backed county rows to support that routing.
Retest lane
Retest lane: 2.0-3.9 pCi/L deserves more caution in the elevated/high county set than in lower-signal counties. The hub should send those users to county pages before product or cost paths.
Best county pages to open first
Start with these local evidence pages
Ranked by measured burden, 4.0+ share, test volume, and whether the EPA zone understates the measurement signal.
Lincoln County
CDC Tracking
51.4% 4.0+ - 19.3 pCi/L primary - 51 tests
Lincoln County is a first-click page: 51.4% of reported tests at or above 4.0 and 19.3 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Lewis and Clark County
CDC Tracking
61.8% 4.0+ - 12.3 pCi/L primary - 333 tests
Lewis and Clark County is a first-click page: 61.8% of reported tests at or above 4.0 and 12.3 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Silver Bow County
CDC Tracking
70.1% 4.0+ - 8.8 pCi/L primary - 106 tests
Silver Bow County is a first-click page: 70.1% of reported tests at or above 4.0 and 8.8 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Lake County
CDC Tracking
40.3% 4.0+ - 7.8 pCi/L primary - 90 tests
Lake County is a first-click page: 40.3% of reported tests at or above 4.0 and 7.8 pCi/L primary result. Route no-reading users to a test now and 4.0+ users to quote or credit planning.
Highest 4.0+ share
Primary result 8.8 pCi/L - high-end 48.5 pCi/L
CDC Tracking
Primary result 12.3 pCi/L - high-end 1100.0 pCi/L
CDC Tracking
Primary result 19.3 pCi/L - high-end 375.3 pCi/L
CDC Tracking
Primary result 5.9 pCi/L - high-end 202.8 pCi/L
CDC Tracking
Primary result 6.2 pCi/L - high-end 145.0 pCi/L
CDC Tracking
Highest high-end reading
4.0+ share 61.8% - primary result 12.3 pCi/L
CDC Tracking
4.0+ share 51.4% - primary result 19.3 pCi/L
CDC Tracking
4.0+ share 37.8% - primary result 7.3 pCi/L
CDC Tracking
4.0+ share 44.6% - primary result 5.9 pCi/L
CDC Tracking
4.0+ share 44.6% - primary result 6.2 pCi/L
CDC Tracking
Most reported tests
4.0+ share 44.6% - primary result 5.9 pCi/L
CDC Tracking
4.0+ share 42.8% - primary result 5.6 pCi/L
CDC Tracking
4.0+ share 42.4% - primary result 4.3 pCi/L
CDC Tracking
4.0+ share 44.6% - primary result 6.2 pCi/L
CDC Tracking
4.0+ share 37.8% - primary result 7.3 pCi/L
CDC Tracking
Measured pattern
Among 10 visible counties with measurement tables, 9 land in the high measured-burden band and 10 land in high or elevated measured-burden bands. That lets this hub rank counties by observed test distribution instead of repeating the EPA map.
Map vs measurements
1 elevated measured counties are not EPA Zone 1. Those are the pages where the actual test distribution matters more than a map-only answer.
Source confidence
The measured rows shown here use CDC Tracking. This is still official evidence, but the hub should keep source caveats visible until a stable state table is available.
Already Tested
View Montana Cost Estimates
If you already have a radon result, skip the directory and move straight to local price guidance.
Understand the Number
2.0 vs 4.0 vs 8.0 pCi/L
Use the parent levels guide if you need the plain-English meaning of a radon result before browsing counties.
Need a Number First
Read the Testing Guide
Use the fastest valid radon test setup before you compare quotes or ask whether mitigation is worth it.
Browse Counties
Jump to the Directory
Open your county to see its EPA zone, testing meaning, and the point where mitigation becomes worth pricing.
Official State Resource
Montana radon program and rules
Use the state program link to verify local radon guidance, disclosure language, and contractor credential expectations before you act on an estimate.
Disclosure note
Montana does not have specific radon disclosure requirements. General property disclosure laws apply.
Credential note
Montana does not require state licensing for radon professionals.
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