There are 5 US Post Offices in Coal County serving a total of 5,710 residents equating to 1,142 residents per post office. It's estimated that approximately 9,114 packages are handled across the 5 county post offices annually. Coal County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 5,925. Its county seat is Coalgate."