Adelphi is an unincorporated area and census-designated place in Prince George's County, Maryland. It includes the communities of Adelphi Hills, Buck Lodge, Chatham, Cool Spring Terrace, and White Oak Manor. Its population at the 2000 census was 14,998.
The Harry Diamond Laboratories were established in 1971 and continue to this day as Adelphi Laboratory Center and Army Research Laboratory (ARL). Other nearby federal facilities include the National Archives at College Park and headquarters of the Food and Drug Administration.
According to the 2000 census, the town was 29.48% White, 39.83% African American, with the remaining being people of other races. 25.74% of the population were people of Hispanic origin.