US Environmental Protection Agency (EPA) - www.epa.gov/radon
Here you will find a nationwide map of radon zones, a link to the Consumers Guide to Radon Reduction and a link to the Home Buyer's/Seller's Guide to Radon
ANSI/AARST Protocol for Conducting Measurements of Radon and Radon Decay Products in Homes - www.standards.aarst.org/MAH-2019/index.html
This document is the current standard of practice which specifies procedures and minimum requirements for measuring radon concentrations in single-family residences and for determining if radon mitigation is necessary to protect its occupants.
American Association of Radon Scientists and Technologists (AARST) Radon Report Card for the State of Illinois - https://aarst.org/Report-Cards/IL-Report-Card.html
The purpose of the Report Card is to facilitate evaluation and rating of state radon policies and risk according to objective criteria and publicize the results. AARST anticipates that this resource will assist consumers, policy makers, public advocates, soil gas professionals, radon programs, researchers, and other health and housing stakeholders in accomplishing expanded and improved efforts to stop radon in the nation’s homes, schools, and other buildings. The Report Card will be updated annually.