Hattiesburg is a city in the U.S. state of Mississippi, located primarily in Forrest County (where it is the county seat and largest city) 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.

Development of the interior of Mississippi took place primarily after the American Civil War. Before that time, only properties along the major rivers were developed as plantations. Founded in 1882 by civil engineer William H. Hardy, Hattiesburg was named in honor of Hardy's wife Hattie. The town was incorporated two years later with a population of 400. Hattiesburg's population first expanded as a center of the lumber and railroad industries, from which was derived the nickname "The Hub City". It now attracts newcomers because of the diversity of its economy, strong neighborhoods, and the central location in South Mississippi.

Hattiesburg is home to the University of Southern Mississippi (founded as Mississippi Normal College, for the training of teachers) and William Carey University (formerly William Carey College). South of Hattiesburg is Camp Shelby, the largest US National Guard training base east of the Mississippi River, which hosts up to 100,000 National Guardsmen and Reservists annually.