Idylwood is a census-designated place (CDP) in Fairfax County, Virginia, United States. The population was 17,954 as of the 2020 census. It originally developed as a suburban community along the route of the Washington and Old Dominion Railroad, and later along Virginia State Route 7. The construction of the Capital Beltway in the 1960s, and I-66 and the Orange Line of the Washington Metrorail system in the 1980s, as well as the concurrent development of nearby Tysons Corner into Washington's leading suburban business district, led to the development of several apartment, townhouse, and small-lot single-family housing complexes, as well as the high-rise Idylwood Towers condominium, in the portion of Idylwood lying to the north of I-66. The area to the south of I-66 remains primarily large-lot single-family.

Virginia State Route 7 (VA 7) is a major primary state highway and busy commuter route in northern Virginia, United States. It travels southeast from downtown Winchester to SR 400 in downtown Alexandria. Its route largely parallels those of the Washington & Old Dominion Trail and the Potomac River. Between its western terminus and Interstate 395 (I-395), SR 7 is part of the National Highway System. In 1968, the Virginia State Highway Commission designated the road as the "Harry Flood Byrd Highway" between Alexandria and Winchester to commemorate Harry F. Byrd Sr. (1887–1966).