The Valley

San Mateo County is a county located in the San Francisco Bay Area of the U.S. state of California. It covers most of the San Francisco Peninsula just south of San Francisco, and north of Santa Clara County. San Francisco International Airport is located at the northern end of the county, and Silicon Valley begins at the southern end. The county seat is Redwood City. It is strongly Democratic and ethnically diverse. The county's built-up areas are mostly suburban with some areas being very urban, and are home to several corporate campuses.