Hattiesburg is the 5th most populous city in the U.S. state of Mississippi, located primarily in Forrest County and extending west into Lamar County. The city population was 45,989 at the 2010 census, with the population now being 48,730 in 2020. Hattiesburg is the principal city of the Hattiesburg Metropolitan Statistical Area, which encompasses Covington, Forrest, Lamar, and Perry counties. The city is located in the Pine Belt region.