It serves a population of approximately 1,141,620 residents within an area of approximately 400 square miles (1,000 km2) in Fairfax County, a Northern Virginian suburb of Washington, D.C.[1] It is one of the largest Sheriff's Offices in Virginia with nearly 600 sworn deputies.

Sheriff Stacey A. Kincaid and her deputies also serves the 65,000 residents of the City of Fairfax and towns of Herndon and Vienna.

Sheriff Kincaid helped launch Diversion First so that incarceration would no longer be the default solution for individuals experiencing a mental health crisis.

In addition to sworn staff, the Sheriff’s Office employs civilian nurses, correctional technicians and administrative personnel to support the agency’s mission.

On July 1, 1940, the Fairfax County Police Department became a separate agency under the control of Board of Supervisors.