This is the EPA page with links to each state’s official EPA data.
Be aware that readings are only for gamma radiation, not for beta or alpha.
Also, EPA readings can be significantly less than independent readings; EPA even says: “EPA posts monitoring results after checking to ensure they meet quality standards”. How much do they fudge the data?
There are sometimes flat lines or gaps in data. Members of the public who monitor radiation say that these gaps often occur when radiation readings are rising. Taking rad monitors offline means the public has no way of knowing how high these spikes are.