Sometimes the simplest tools are the most useful.
Such is the case with Rootsweb’s US Town and County Database. This handy little tool allows US researchers to find the county or parish (depending on the organization of local government within a state) in which an ancestor lived. Handily, knowing the county or parish allows one to locate many of the more commonly-used historical and genealogical records.
If only the town name is known, that’s ok! Inputting the town’s name without the state will bring up a list of counties and their respective states, thus dramatically narrowing one’s search for possible origins.