There are 3 US Post Offices in Greer County serving a total of 6,252 residents equating to 2,084 residents per post office. It's estimated that approximately 9,979 packages are handled across the 3 county post offices annually. Greer County is a county located along the southwest border of the U.S. state of Oklahoma. As of the 2010 census, the population was 6,239. Its county seat is Mangum. From 1860 to 1896, the state of Texas claimed an area known as Greer County, Texas, which included present-day Greer County along with neighboring areas. In 1896 it was designated as a county in Oklahoma Territory under a ruling by the US Supreme Court. The rural Greer County is home to Quartz Mountain Nature Park, near the community of Lone Wolf, Oklahoma (known until 2002 as Quartz Mountain State Park). It is also home to the Oklahoma State Reformatory, located in Granite. Its population has declined since 1930 due to changes in agriculture and migration to cities for work."