US Post Office-Frankfort is a historic post office building located at Frankfort in Herkimer County, New York, United States. It was built in 1940–1941, and is one of a number of post offices in New York State designed by the Office of the Supervising Architect of the Treasury Department, Louis A. Simon. It is a one-story, five-bay, steel frame building on a raised foundation in the Colonial Revival style. It features a three-bay central pavilion surmounted by a slate-covered hipped roof. The interior features a 1942 wood relief by artist Albert Wein titled "Growth."

It was listed on the National Register of Historic Places in 1989.