Forrest County is a county located in the U.S. state of Mississippi. As of the 2020 census, the population was 78,158. Its county seat and largest city is Hattiesburg. The county was created from Perry County in 1908 and named in honor of Nathan Bedford Forrest, a Confederate general in the American Civil War and the first Grand Wizard of the Ku Klux Klan. Forrest County is part of the Hattiesburg, MS Metropolitan Statistical Area.