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 2014, the population was estimated to be 1,118,883, making it the most populous jurisdiction in the Commonwealth of Virginia, 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 Fairfax.