Fairfax County, officially the County of Fairfax, is a county in the Commonwealth of Virginia.
As of the 2010 census, the population was 1,081,726, in 2015, it was estimated at 1,142,234,making it the Commonwealth’s most populous jurisdiction, with 13.6% of Virginia’s population. The county is also the most populous jurisdiction in the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area, with 19.8% of the MSA population, as well as the larger Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area, with 13.1% of the CSA population. The county seat is the City of Fairfax, though because it is an independent city under Virginia law, the city of Fairfax is not part of Fairfax County.
Fairfax was the first U.S. county to reach a six-figure median household income and has the second-highest median household income of any local jurisdiction in the United States after neighbor Loudoun County.
The county is home to the headquarters of intelligence agencies such as the Central Intelligence Agency, National Geospatial-Intelligence Agency, and National Reconnaissance Office, as well as the National Counterterrorism Center and Office of the Director of National Intelligence. The county is also home to seven Fortune 500 companies, including three with Falls Church addresses.
According to the U.S. Census Bureau, the county has a total area of 406 square miles (1,050 km2), of which 391 square miles (1,010 km2) is land and 15 square miles (39 km2) (3.8%) is water.
Fairfax County is bounded on the north and southeast by the
Potomac River. Across the river to the northeast is Washington, D.C., across the river to the north is Montgomery County, Maryland, and across the river to the southeast are Prince George’s County, Maryland and Charles County, Maryland. The county is partially bounded on the north and east by Arlington County and the independent cities of Alexandria and Falls Church. It is bounded on the west by Loudoun County, and on the south by Prince William County.
Most of the county lies in the Piedmont region, with rolling hills and deep stream valleys such as Difficult Run and its tributaries. West of Route 28, the hills give way to a flat, gentle valley which stretches west to the Bull Run Mountains in Loudoun County. Elevations in the county range from sea level along the Potomac River to 200–500 feet (60–150 m) in the hills.
Several major highways run through Fairfax County, including the Capital Beltway (Interstate 495), Interstate 66, Interstate 95, and Interstate 395. The American Legion Bridge connects Fairfax to Montgomery County, Maryland. The George Washington Memorial Parkway, Dulles Toll Road, and Fairfax County Parkway are also major arteries. Other notable roads include Braddock Road, Old Keene Mill Road, Little River Turnpike, State Routes 7, 28, and 123, and US Routes 1, 29, and 50.