There are 9 US Post Offices in Grant County serving a total of 7,337 residents equating to 815 residents per post office. It's estimated that approximately 11,711 packages are handled across the 9 county post offices annually. Grant County is a county located in the U.S. state of Oregon. As of the 2010 census, the population was 7,445. The county seat is Canyon City. It is named for President Ulysses S. Grant, who served as an army officer in the Oregon Territory, and at the time of the county's creation was a Union general in the American Civil War. Grant County is included in the 8 county definition of Eastern Oregon."