You can use the database at QRZ.com, although it won't be 100% accurate.
http://www.qrz.com/db/?cmd=1Type in a search of the county you want:
county: Hays
and it will prompt you for which state, if there are several counties with that same name in different states.
I assume the county is guessed at by what town is in the listed address, although some hams may have an address in a town which is across a county line from where their home is.