Hattiesburg is a city in Forrest County, Mississippi. The population was 44,779 at the 2000 census (51,993 according to 2008 estimate). It is the county seat of Forrest County. In recent years the city has grown to include a portion of eastern Lamar County. It is the principal city of the Hattiesburg, Mississippi, Metropolitan Statistical Area which encompasses Forrest, Lamar and Perry counties. Founded in 1882 by pioneer lumberman and civil engineer William H.