Poston is a census-designated place (CDP) in La Paz County, Arizona, United States, in Parker Valley. The population was 389 at the 2000 census. During World War II, Poston was the site of the Poston War Relocation Center, which was one of the United States' largest Japanese internment camps, where over 17,000 Japanese-Americans were held over a three-year period. The camp sites are now home to a monument dedicated to those who died and suffered while in internment.