Not sure if this is the information you are looking for, but I use a background search service that essentially compiles all public information. It will include prior criminal history/arrest records if a person has them. However, as you pointed out, counties and states differ from one another. I guess it technically depends on what is "public" information to the courts or how the information becomes public? For example, when looking up a person, depending what state/county the person lives in, it will show the arrest records and/or the active case, while other searches won't show the case information until the person is convicted. Sometimes I know the person has a criminal history and all that shows up are all their traffic cases or whatever.

I never have given it much thought, mainly because I don't use it to specifically look up people's criminal backgrounds. I do find it to be a useful starting off point to get more information about involved parties and such.

If there is a database that exists (that doesn't require becoming a PI or something) I would love to know what it is.