There are 6 US Post Offices in Grant County serving a total of 4,266 residents equating to 711 residents per post office. It's estimated that approximately 6,809 packages are handled across the 6 county post offices annually. Grant County is a county located on the northern border of the U.S. state of Oklahoma. As of the 2010 census, the population was 4,527. Its county seat is Medford. Originally designated as part of the Cherokee Outlet, it was named County L in Oklahoma Territory at the time of its opening to non-Indian settlement. A county election renamed it for U.S. President Ulysses S. Grant.