Triangle is a census-designated place (CDP) in Prince William County, Virginia, United States. The population was 5,500 at the 2000 census. It is bounded to the south by the Quantico Marine Corps Base, which surrounds the town of Quantico. It is bounded to the north and west by the town of Dumfries. It is bounded to the west by Prince William Forest Park and to the east by the Potomac River.
According to the United States Census Bureau, the CDP has a total area of 2.6 square miles (6.8 km²), all of it land.
As of the census of 2000, there were 5,500 people, 2,196 households, and 1,341 families residing in the CDP. The population density was 2,088.5 people per square mile (807.4/km²). There were 2,318 housing units at an average density of 880.2/sq mi (340.3/km²). The racial makeup of the CDP was 61.07% White, 28.33% African American, 0.49% Native American, 2.87% Asian, 0.11% Pacific Islander, 3.58% from other races, and 3.55% from two or more races. Hispanic or Latino of any race were 7.42% of the population.