Post Office Since 1816:
The McAlesters' A Field Guide to American Houses describes this design as a Gable Front Family Folk house common on the East Coast of the U.S. before the Civil War. The pediment and columns suggest a Greek Revival influence, which is often found in American Antebellum Architecture.
The Hinsdale, New Hampshire post office has been operating in this building since 1816. This is the oldest continuously working U.S. Post Office in the same building. Is this oddity enough to call it "historic?"
Sources: McAlester, Virginia and Lee. Field Guide to American Houses. New York. Alfred A. Knopf, Inc. 1984, pp. 89-91; and USPS Facts page