Fairfax County is a county in Northern Virginia, in the United States. Per the 2010 Census, the population of the county is 1,081,726, making it the most populous jurisdiction in the Commonwealth of Virginia, with 13.5% of Virginia's population. The county is also the most populous jurisdiction in the Washington Metropolitan Area, with 19.8% of the MSA population, as well as the larger Baltimore � Washington Metropolitan Area, with 13.1% of the CSA population.
Fairfax was the first county in the United States 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 half of the metropolitan area's Fortune 500 companies.