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RADON411

Data

Data sources

Every source behind Radon411's numbers and guides, by name, grouped by what it feeds: predicted maps, measured test results, the figures we calculate, the guidance and the directory.

Updated October 2, 2026

Updated October 2, 2026

At a glance

Where the numbers come from

Radon411 keeps three kinds of number apart, and every source below feeds exactly one of them, or the guides and the directory.

2
Predicted maps: what an area is expected to have, never a measurement
7
Measured datasets: tests that were actually carried out
94
Publications behind the guides, from 27 publishers

Predicted

Predicted: maps of expected radon

A classification for a whole area, produced from geology and past measurements. It says nothing certain about any one home.

Updated October 19, 2026

  • U.S. Environmental Protection Agency

    EPA Map of Radon Zones

    On Radon411
    The EPA zone on every county and state report, and the county map
    Covers
    All U.S. counties
    Licence
    U.S. Government Work, public domain; redistribute with attribution to EPA.

  • U.S. Geological Survey

    USGS Geologic Radon Potential Map of the United States (2025)

    On Radon411
    The geologic radon potential on county reports, as the share of each county in each class
    Covers
    United States: conterminous states, Alaska and Hawaii (three layers)
    Licence
    CC0 1.0 Universal, public domain dedication; no restriction on redistribution.

Measured

Measured: radon tests that were carried out

Results reported to a public health agency, shown at the geography the agency published them for. A state's figures are never mixed with CDC's.

  • Centers for Disease Control and Prevention

    Updated October 19, 2026

    CDC Environmental Public Health Tracking, Radon Testing

    Covers
    States and counties that report to CDC EPHT radon testing measures

  • Colorado Department of Public Health and Environment (CDPHE), Colorado Environmental Public Health Tracking

    Updated October 19, 2026

    Radon data (county results)

    Covers
    CO: county; 2005 to 2025, evaluated across all years available

  • Michigan Department of Environment, Great Lakes, and Energy (EGLE), Indoor Radon Program

    Updated October 19, 2026

    Michigan Indoor Radon Results

    Covers
    MI: zip; approximately the preceding 10 years, refreshed at least quarterly

  • Minnesota Department of Health (MDH), Minnesota Environmental Public Health Tracking

    Updated October 19, 2026

    Radon Testing (MN Public Health Data Access Portal)

    Covers
    MN: county, state; 2016 to 2025

  • Nevada Bureau of Mines and Geology and University of Nevada Cooperative Extension (Nevada Radon Education Program)

    Updated October 19, 2026

    Radon averages by ZIP code (NBMG Hazards: Radon_Average)

    Covers
    NV: zip; 1989 through 2015

  • New York State Department of Health, Bureau of Environmental Radiation Protection

    Updated October 19, 2026

    Indoor air radon testing data (Environmental Public Health Tracker)

    Covers
    NY: county, state; five-year periods from 2000-2004 to 2015-2019

  • Pennsylvania Department of Environmental Protection (DEP), Bureau of Radiation Protection

    Updated October 2, 2026

    Radon Test Data by Zip Code

    Covers
    PA: zip; not stated in DEP's report

Where a state reports fewer than five tests for a place, Radon411 shows the count but not the figures. Every state dataset's terms of reuse were checked before it was used; the licences are in the last section.

Calculated

Calculated: what Radon411 works out

Figures Radon411 derives from published data, each labelled as calculated, with its method on the methodology page. These are the places and populations it works from.

U.S. Census Bureau

  • Cartographic boundary files, through the us-atlas package

    Updated October 19, 2026

    On Radon411
    Every state and county, its boundary and code; the neighbours and map points Radon411 works out from them. Land area is not taken from the boundaries: it is the U.S. Census Bureau's own figure for land, from its 2020 Census Gazetteer Files, Counties (national file)
    Covers
    56 states and territories, 3,231 counties
    Licence
    U.S. government work, public domain; the us-atlas packaging is under the ISC licence

  • Census 2020 ZCTA to County Relationship File

    Updated October 4, 2026

    On Radon411
    Which county a ZIP code area falls in
    Covers
    All 2020 ZCTAs and the 2020 counties they overlap
    Licence
    U.S. Government Work, public domain; redistribute with attribution to the U.S. Census Bureau.

  • Census 2020 Place Reference Codes (incorporated places)

    Updated October 4, 2026

    On Radon411
    The cities and towns that have their own report
    Covers
    Incorporated places in the 2020 place reference file, 50 states, DC and Puerto Rico where listed
    Licence
    U.S. Government Work, public domain; redistribute with attribution to the U.S. Census Bureau.

  • Census Population Estimates Program, county and state totals

    Updated October 4, 2026

    On Radon411
    State and county population on reports
    Covers
    50 states, the District of Columbia and their counties (Puerto Rico is published separately)
    Licence
    U.S. Government Work, public domain; redistribute with attribution to the U.S. Census Bureau.

  • Census Population Estimates Program, incorporated place totals

    Updated October 4, 2026

    On Radon411
    City population on city reports
    Covers
    Incorporated places in the 50 states and the District of Columbia
    Licence
    U.S. Government Work, public domain; redistribute with attribution to the U.S. Census Bureau.

Guidance

Guidance: what the guides and answers are written from

Every fact in a guide or answer is checked against the publication's own words before it is published. Open a publisher to see its publications and when each was last checked.

  • U.S. Environmental Protection Agency

    The action level, the testing and fixing advice, and the guides built on them

    Checked October 19, 2026

  • Kansas State University

    Background for the guides

    Checked October 19, 2026

Checked October 19, 2026

EPA43 publications

CDC10 publications

Minnesota Department of Health5 publications

PubChem (NIH)5 publications

Iowa HHS3 publications

Idaho Department of Health and Welfare2 publications

National Cancer Institute2 publications

New Jersey Department of Environmental Protection2 publications

Pennsylvania Department of Environmental Protection2 publications

Washington State Department of Health2 publications

Wisconsin Department of Health Services2 publications

AARST1 publication

ATSDR (CDC)1 publication

HHS1 publication

HUD Archives1 publication

IARC1 publication

Illinois Emergency Management Agency and Office of Homeland Security1 publication

Maine CDC1 publication · not yet checked

  • Landlords Disclosure To Tenants Of Radon Gas Hazards In A Residential Rental Property (HHE-810, PDF)

    Not yet checked · Used in Radon Action Month checklist

Mississippi State Department of Health1 publication

Missouri Department of Health and Senior Services1 publication

Nebraska DHHS1 publication

NIEHS (NIH)1 publication

North Carolina Division of Public Health1 publication

Royal Society of Chemistry1 publication

Utah DEQ1 publication

Virginia Department of Health1 publication

WHO1 publication

Directory

The directory and the state program cards

Professionals are listed from the lists state agencies publish, and checked against the national certification bodies.

The state radon program card on every state and county reportChecked October 19, 2026

  • Radon411, compiled from individual state agency pages

Checking a listed professional's NRPP certification before it is marked verifiedChecked October 19, 2026

  • National Radon Proficiency Program (a program of AARST)

Checking a listed professional's NRSB certification before it is marked verifiedChecked October 19, 2026

  • National Radon Safety Board

The state radon program card, checked against each state's own pageChecked October 19, 2026

  • Various state environmental and health agencies

The professionals that state licenses, in the directory

  • Illinois Emergency Management Agency (IEMA)Checked October 19, 2026
  • Iowa Department of Health and Human Services, Bureau of Radiological HealthChecked October 19, 2026
  • Pennsylvania Department of Environmental Protection, Bureau of Radiation ProtectionChecked October 19, 2026
  • Nebraska Department of Health and Human Services, Radon ProgramChecked October 19, 2026
  • Florida Department of Health, Radon ProgramChecked October 19, 2026
  • Kansas Department of Health and Environment, Kansas Radon ProgramChecked October 12, 2026
  • Colorado Department of Regulatory Agencies, Office of Radon ProfessionalsChecked October 19, 2026
  • Minnesota Department of HealthChecked October 19, 2026
  • New Jersey Department of Environmental ProtectionChecked September 25, 2026
  • Kentucky Board of Radon SafetyChecked September 25, 2026
  • Indiana Department of HealthNot checked
  • Ohio Department of Health, Radon Education and Licensing ProgramChecked October 19, 2026
  • Rhode Island Department of HealthChecked October 19, 2026
  • West Virginia Office of Environmental Health Services, Radiation, Toxics and Indoor Air DivisionChecked October 19, 2026
  • Maine Center for Disease Control and Prevention, Radiation Control ProgramNot checked
  • California Department of Public Health, Indoor Radon ProgramChecked October 19, 2026
  • New Hampshire Department of Health and Human ServicesNot checked
  • Connecticut Department of Public Health, Radon ProgramNot checked
  • Utah Department of Environmental Quality, Division of Waste Management and Radiation ControlNot checked
  • Virginia Department of Health, Indoor Radon ProgramNot checked

The professionals that state's radon program lists, in the directory

  • Connecticut Department of Public Health, Radon ProgramChecked October 4, 2026
  • New York State Department of HealthChecked October 4, 2026
  • Oregon Health Authority, Radon ProgramChecked October 4, 2026
  • Nevada Radon Education Program, University of Nevada, Reno ExtensionChecked October 4, 2026
  • North Dakota Department of Environmental QualityChecked October 4, 2026
  • Delaware Division of Public Health, Radon ProgramNot checked
  • Colorado Department of Public Health and Environment, as printed by CSU Extension, Teller CountyNot checked

The radon businesses a local health department lists, in the directory

  • Boulder County Public HealthNot checked
  • Gilpin County Public HealthNot checked
  • City of AspenNot checked
  • Howard County Health Department, IndianaChecked October 4, 2026
  • Michigan EGLE, as published by the Oakland County Health DivisionChecked October 4, 2026

Licences

Attributions a licence requires

Most of what Radon411 uses is public domain. These are the sources whose licence asks for a credit or a notice, given here in the licence's own terms.

Radon averages by ZIP code (NBMG Hazards: Radon_Average)

Credit
Nevada Bureau of Mines and Geology, University of Nevada, Reno
Licence
Creative Commons Attribution 4.0 International (CC BY 4.0), creativecommons.org/licenses/by/4.0/
Notice
© Copyright 2010 The University of Nevada, Reno. The data are supplied as-is: the Nevada Bureau of Mines and Geology, the University of Nevada, Reno and the Nevada System of Higher Education make no warranties of any kind. The material: gisweb.unr.edu/nbmg/rest/services/Hazards/Radon_Average/MapServer
Changes
Radon411 rounds each average to one decimal place for display.
Why it is here
CC BY 4.0, section 3(a)(1)(C): “indicate the Licensed Material is licensed under this Public License, and include the text of, or the URI or hyperlink to, this Public License”.

us-atlas, the packaging of the Census boundary files the maps are drawn from

Credit
Michael Bostock
Licence
ISC licence
Notice
Copyright 2013-2019 Michael Bostock. Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
Why it is here
ISC licence: “provided that the above copyright notice and this permission notice appear in all copies”.

The EPA, CDC and Census Bureau material is a U.S. government work and the USGS map is dedicated to the public domain under CC0; each is named in its group above.

The national map’s land, lakes, coastlines and the borders of Canada and Mexico are drawn from Natural Earth’s 1:10m data, and the terrain shading over the counties from the Terrain Tiles open elevation dataset on Amazon Web Services. The county and state outlines are the U.S. Census Bureau’s 2018 cartographic boundary files at 1:500,000. Radon411 serves all of them itself, as map tiles.

Our images

Reusing our images

The figures, charts and maps Radon411 makes are free to reuse under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence.

  • What you may do

    You may copy, share and adapt them, for any purpose, commercial included, as long as you credit us.

  • The credit line

    RADON411, linked to the page the image came from: for example, “Image: RADON411”, with RADON411 linking to the guide or state report where you found it.

The facts in each image come from the public agencies named in its source line. Photographs on the site that we did not take keep their own licences, given on the about page.

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