Countryside is a census-designated place in Loudoun County, Virginia, United States. The population as of the 2010 census was 10,072. It is located approximately 27 mi northwest of Washington and is bounded by the Potomac River to the north, and by Route 7 (Leesburg Pike) to the south. Located in eastern Loudoun County, it is about 9 mi north of Washington Dulles International Airport. It is bordered by the community of Cascades to the east and by Dulles Town Center to the south, across Route 7.