There are 6 US Post Offices in Simpson County serving a total of 27,758 residents equating to 4,626 residents per post office. It's estimated that approximately 44,305 packages are handled across the 6 county post offices annually. Simpson County is a county located in the U.S. state of Mississippi. Its western border is formed by the Pearl River, an important transportation route in the 19th century. As of the 2010 census, the population was 27,503. The county seat is Mendenhall. The county is named for judge Josiah Simpson. Simpson County is part of the Jackson, MS Metropolitan Statistical Area. Spencer Myrick, a member of both houses of the Louisiana State Legislature, and his brother, Bill, a Country music figure in Odessa, Texas, were born in Simpson County. They were reared in West Carroll Parish in northeastern Louisiana."