Fairfax County, officially the County of Fairfax, is a county in the Commonwealth of Virginia. It is part of Northern Virginia and borders both the city of Alexandria and Arlington County and forms part of the suburban ring of Washington, D.C., the nation's capital.

Population: 1.138 million (2022)
Area: 406 mi²
Head: Chairman Jeffrey C. McKay fairfaxcounty.gov
Area code: 703, 571
Congressional districts: 8th, 10th, 11th
Founded: June 19, 1742
Largest town: Herndon