The average national indoor radon level is 1.3 pCi/L. (FAQ: What is a picocurie?)
The average indoor radon levels of McHenry County, as determined by radon test results from Air Chek, is 3.8 pCi/LLocal News
Results under 2 pCi/L
Results between 2 and 3.9 pCi/L
Results 4 pCi/L and above
Additional information about radon levels in McHenry County may be available through this website.