Dahlgren is a census-designated place (CDP) in King George County, Virginia, United States. The population was 2,655 at the 2010 census, a large increase from the 997 reported in 2000.
Since 1918, Dahlgren has been the site of a U.S. Naval base named for Rear Admiral John A. Dahlgren. It was then the "U.S. Naval Proving Ground" but was renamed, after 1950, "U.S. Naval Weapons Laboratory", in 1974, the "Naval Surface Weapons Center","in 1987 the "Naval Surface Warfare Center", and around 1990, as the "U.S. Naval Surface Warfare Center Dahlgren Division (NSWCDD)". In 2006, it was renamed "Naval Support Activity-South Potomac (NSA-SP)", with NSWCDD becoming a tenant command of the base. The "U.S. Naval Space Surveillance Systems" command was located at that base, but that responsibility was transferred to the Air Force in 2004. The AEGIS Training and Readiness Center is currently a tenant command at NSA-SP. The 1.7-mile long, narrow two-lane Governor Harry W. Nice Memorial Bridge funnels interstate traffic across the wide Potomac River at Dahlgren, offering an alternative to using Interstate 95.