There are 3 US Post Offices in Marshall County serving a total of 15,840 residents equating to 5,280 residents per post office. It's estimated that approximately 25,282 packages are handled across the 3 county post offices annually. Marshall County is a county located on the south central border of Oklahoma. As of the 2010 census, the population was 15,840. Its county seat is Madill. The county was created at statehood in 1907 from the former Pickens County of the Chickasaw Nation. It was named to honor the maiden name of the mother of George Henshaw, a member of the 1906 Oklahoma Constitutional Convention. The county and it's cities are part of the Texoma region."