Hybla Valley is a census-designated place in Fairfax County, Virginia, United States, south of Alexandria. The population was 15,801 at the 2010 census, down from 16,721 in 2000 due to a reduction in area, resulting from some of the eastward neighborhoods including much of Hollin Hills being moved to the Fort Hunt CDP. The population increased to 16,319 in the 2020 census.