Fairfax County, officially the County of Fairfax, is a county in the Commonwealth of Virginia. With a population of 1,150,309 as of the 2020 census, it is the most populous county in Virginia, the most populous jurisdiction in the Washington metropolitan area, and the most populous location in the Washington–Baltimore combined statistical area. The county seat is Fairfax; however, because it is an independent city under Virginia law, the city of Fairfax is not part of the county.
The county is part of the Northern Virginia region and forms part of the suburban ring of Washington, D.C., the nation's capital. The county is predominantly suburban with some urban and rural pockets. It borders Montgomery County, Maryland to its north, Falls Church, Alexandria, Arlington County, and Prince George's County, Maryland to its east, Charles County, Maryland to its southeast, Prince William County to its southwest, and Loudoun County to its northwest.