Solano County is a county located in the U.S. state of California. As of the 2020 census, its population was 453,491. The county seat is Fairfield. Solano County comprises the Vallejo–Fairfield metropolitan statistical area, which is also included in the San Jose–San Francisco–Oakland, combined statistical area. Solano County is the northeastern county in the nine-county San Francisco Bay Area region. A portion of the South Campus at the University of California, Davis, is in Solano County.