Alameda County ( AL-ə-MEE-də) is located in the state of California in the United States. As of the 2010 census, the population was 1,510,271, making it the 7th-most populous county in the state and 20th most populous nationally. The county seat is Oakland. Alameda County is in the San Francisco Bay Area, occupying much of the East Bay region. The Spanish word alameda means either "a grove of poplars...or a tree lined street." The name was originally used to describe the Arroyo de la Alameda. The willow and sycamore trees along the banks of the river reminded the early Spanish explorers of a road lined with trees. Although a strict translation to English might be "Poplar Grove Creek," the name of the principal stream that flows through the county is now simply "Alameda Creek." Alameda County is part of the San Francisco–Oakland–Berkeley, CA Metropolitan Statistical Area, and the San Jose–San Francisco–Oakland, CA Combined Statistical Area.