Belvoir was the plantation and estate of colonial Virginia's prominent William Fairfax family. Operated with the forced labor of enslaved people, it was located on the west bank of the Potomac River on the present site of Fort Belvoir in Fairfax County, Virginia.

Fort Belvoir is a United States Army installation and a census-designated place (CDP) in Fairfax County, Virginia, United States. It was developed on the site of the former Belvoir plantation, seat of the prominent Fairfax family for whom Fairfax County was named. It was known as Camp A. A. Humphreys from 1917 to 1935 and Fort Belvoir afterward.