Silicon Valley is in a state.
Oakland [ ˈoʊklənd ] is the largest city and the county seat of Alameda County , California , United States . San Mateo County, California . oʊ ] ; Spanish for `` Saint Matthew '' ) is a county located in the U.S. state of California . Silicon Valley is a nickname for the southern portion of the San Francisco Bay Area , in the northern part of the U.S. state of California . As more high-tech companies were established across the Santa Clara Valley , and then north towards the Bay Area 's two other major cities , San Francisco and Oakland , the `` Silicon Valley '' name eventually came to refer to all high-tech businesses in the region .