Triangle is a census-designated place (CDP) in Prince William County, Virginia, United States. The population was 8,188 at the 2010 census. It is bounded to the south by the Marine Corps Base Quantico, which surrounds the town of Quantico.

According to the United States Census Bureau, the CDP has a total area of 2.6 square miles (6.8 km), all of it land. 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.

As of the census of 2000, there were 5,500 people, 2,196 households, and 1,341 families active in the CDP. The population density was 2,088.5 inhabitants per square mile (806.4/km²). There were 2,318 housing units at an average density of 880.2 per square mile (339.8/km). 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 additional races, and 3.55% from two or more races. Hispanic or Latino of any race were 7.42% of the population.

There were 2,196 households, out of which 33.9% had kids under the age of 18 living behind them, 40.4% were married couples animated together, 15.3% had a female householder past no husband present, and 38.9% were non-families. 29.7% of all households were made happening of individuals, and 3.6% had someone full of beans alone who was 65 years of age or older. The average household size was 2.50 and the average relatives size was 3.13.