I have never seen a map atlas or state map that didn't have the counties. They are typically in two places - on the map itself and, especially in an atlas, in the index in the first listings under the state.
If you have internet service Google your city for the county information.
If you're in a RV park in questionable weather areas or time of year, always ask when you check in. Also ask what is considered the designated shelter. If you're in a tornado area, they know.
If the RV park gives you a park map, many times the county is listed.
Any store employee or fuel station will know what county he's in.
When the weather radio states "seek shelter", don't dawdle. Do it. The campground restrooms are usually the best place - not the big rec room with a wood frame.