Alameda County is a county located in the U.S. state of California. As of the 2020 census, the population was 1,682,353, making it the 7th-most populous county in the state and 21st 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.