There are 9 US Post Offices in Johnston County serving a total of 10,809 residents equating to 1,201 residents per post office. It's estimated that approximately 17,252 packages are handled across the 9 county post offices annually. Johnston County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 10,957. Its county seat is Tishomingo. It was established at statehood on November 16, 1907 and named for Douglas H. Johnston, a governor of the Chickasaw Nation. Johnston County is part of the Texoma Region."