Oakland is the most populous city in and the county seat of Alameda County, California, United States. A major West Coast port, Oakland is the largest city in the East Bay region of the San Francisco Bay Area, and the third-largest city overall in the Bay Area. With a population of 440,646 in 2020, it serves as the Bay Area's trade center: the Port of Oakland is the busiest port in Northern California, and the fifth- or sixth-busiest in the United States. A charter city, Oakland was incorporated on May 4, 1852, in the wake of the state's increasing population due to the California gold rush.

Oakland's territory covers what was once a mosaic of California coastal terrace prairie, oak woodland, and north coastal scrub. In the late 18th century, it became part of a large rancho grant in the colony of New Spain, and known for its plentiful oak tree stands. Its land served as a resource when its hillside oak and redwood timber were logged to build San Francisco. The fertile flatland soils helped it become a prolific agricultural region. In the 1850s, what became the first campus of the University of California was founded in Oakland, and Oakland was selected as the western terminal of the Transcontinental Railroad in 1869. The following year, Oakland's Lake Merritt became the United States' first officially designated wildlife refuge, now a National Historic Landmark. Following the catastrophic 1906 San Francisco earthquake, many San Francisco citizens moved to Oakland, enlarging the population, increasing its housing stock, and improving its infrastructure. It continued to grow in the 20th century with its port, shipyards, and manufacturing industry.