The county was formed on March 25, 1853, from a large portion of Contra Costa County and a smaller portion of Santa Clara County.

The Spanish word alameda means “a place where poplar trees grow,” A name originally given to the Arroyo de la Alameda (Poplar Grove Creek). The willow and sycamore trees along the banks of the river reminded the early explorers of a road lined with trees, also known as an alameda.

The county seat at the time it was formed was located at Alvarado; it was moved to San Leandro in 1856 where the county courthouse was destroyed by the devastating 1868 quake on the Hayward Fault. The county seat was then re-established in the town of Brooklyn from 1872-1875. Brooklyn is now part ofOakland, which has been the county seat since 1873.

Much of what is now considered an intensively urban region, with major cities, was developed as a trolley car suburb of San Francisco in the late 19th and early 20th centuries. The historical progression from Native American tribal lands to Spanish, then Mexican ranches, then to farms, ranches, and orchards, then multiple city centers and suburbs, is shared with the adjacent and closely associated Contra Costa County.


#45: Site of College of California
#46: Vallejo Flour Mill
#107: Joaquin Miller Home
#241: Livermore Memorial Monument
#246: Rancho San Antonio (Peralta Grant)
#279: Estudillo Home
#285: Peralta Home
#299: Camino of Rancho San Antonio
#334: Mission San Jose
#335: Site of Shell Mound
#440: Alameda Terminal of the First Transcontinental Railroad
#503: Site of First County Courthouse
#510: Francisco Solano Alviso Adobe
#586: Cresta Blanca Winery
#641: Concanno Vineyard
#642: Leland Stanford Winery
#676: Site of Saint Mary’s College
#694: Church of St. James The Apostle

#768: Site of Nation’s First Successful Beet Sugar Factor
#776: Site of First Public School in Castro Valley
#849: Mills Hall
#884: Paramount Theatre
#896: First Unitarian Church of Oakland
#908: Berkeley City Club
#925: Peralta Hacienda Site
#946: University of California, Berkeley Campus
#954: Croll Building
#957: Wente Bros. Winery
#962: Site of Blossom Rock Navigation Trees
#968: Site of the China Clipper Flight Departure
#970: Rainbow Trout Species Identified
#986: Piedmont Way
#1025: Ukrania, Site of Agapius Honcharnenko Farmstead
#1027: Pardee Home
#1029: USS Hornet
#1036: Coast Guard Lightship WLV 605 -Relief