Hi SuzanneTF1
I have used the plugin Piclayer to JOSM manually trace selected information from screenshots of such sources, but it is laborious.

I should note that while the underlying coordinates of most geographic features are not copywritable, the maps certainly are due to the intellectual work of compiling them.  So if you want to do more than selected research of particular objects from this source, you likely need to ask the county, who could also export the a GIS shapefile, for permission to avoid legal issues.

Exceptions to this are works of US federal employees, which are never copyrighted by law, which is why you will see large imports from TIGER, USGS, and GNIS.