There are 2 US Post Offices in Harper County serving a total of 1,723 residents equating to 862 residents per post office. It's estimated that approximately 2,750 packages are handled across the 2 county post offices annually. Harper County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 3,685, making it the fifth-least populous county in Oklahoma. The county seat is Buffalo. It was created in 1907 from the northwestern part of Woodward County, and named for Oscar Green Harper, who was clerk of the Oklahoma Constitutional Convention."