Mason Neck is a peninsula jutting into the Potomac River in Fairfax County, Virginia, southwest of Washington, D.C.. It is surrounded by Belmont Bay to the west, the Potomac River to the south and east, Gunston Cove to the northeast, and Pohick Bay to the north-northeast. Mason Neck forms the southernmost section of Fairfax County in Northern Virginia. It comprises an area of 20.0 square miles (51.8 km2), two-thirds of which is preserved as parkland by regional, state, and national authorities. The population of the Mason Neck CDP was 2,005 as of the 2010 census.

Gunston Hall is an 18th-century Georgian mansion near the Potomac River in Mason Neck, Virginia, United States. Built between 1755 and 1759 as the main residence and headquarters of a 5,500-acre (22 km2) plantation, the house was the home of the United States Founding Father George Mason. The home is located not far from George Washington's home.