Diamondhead is a city in southeastern Hancock County, Mississippi, United States. The city is located just over 50 miles (80 km) northeast of New Orleans, Louisiana. It is part of the Gulfport−Biloxi Metropolitan Statistical Area. In February 2012, Diamondhead was officially incorporated as a city. At the time of the 2010 census, when Diamondhead was an unincorporated census-designated place, the population was 8,425. The city population, with slightly different boundaries, was estimated at 8,048 in 2019.
On October 25, 1961, NASA announced the formation of the Mississippi Test Facility, now the John C. Stennis Space Center. The center would be located in an area bordering the Pearl River in Hancock County. During and following the construction of the facility, an influx of government workers, contractors, and their families moved into the area.
Much of the land that became Diamondhead had been purchased by Walter Gex, Sr., in 1937 from the Gulf State Paper Company and the Easy Opener Bag Company. Additional land was purchased by Gex, bringing his acquisition to nearly 5,000 acres (2,000 ha). In the late 1960s, D.E.A.R., Inc., later known as the Diamondhead Corporation, a large corporation interested in resort developments, began operations on the Mississippi Gulf Coast, with Diamondhead as its first project.