You will have to define the county or state list yourself. You can not write a checker that says "Find a cache in all counties of Texas", but you can define one that says, "find at least one cache in county x, at least one in county y and so on".
I have a script called X finds in different locations that can check such thing. With one downside. If you require a county names X, and a county named X exists in several countries, it will be accounted for regardless of the county. There are many examples where the same county name exists in different countries.