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 of Oakland, 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.

NameNational LandmarkState LandmarkPoint of InterestOther Designation
Site of College of CaliforniaN/A45N/AN/A
Vallejo Flour Mill7100013146N/AN/A
Joaquin Miller Home66000204107N/AN/A
Livermore Mermorial MonumentN/A241N/AN/A
Rancho San Antonio (Peralta Grant)66000204246N/AN/A
Estudillo HomeN/A279N/AN/A
Peralta House78000654285N/AN/A
Camino of Rancho San AntonioN/A299N/AN/A
Mission San Jose71000131334N/AN/A
Site of Shell MoundN/A335N/AN/A
Alameda Terminal of the First Transcontinental RailroadN/A440N/AN/A
Site of First County CourthouseN/A503N/AN/A
Francisco Solano Alviso AdobeN/A510N/AN/A
Cresta Blanca WineryN/A586N/AN/A
Concannon VineyardN/A641N/AN/A
Leland Stanford WineryN/A642N/AN/A
Site of St. Mary’s CollegeN/A676N/AN/A
Church of St. James the Apostle86003361694N/AN/A
Site of Nation’s First Successful Beet Sugar FactoryN/A768N/AN/A
Site of First Public School in Castro ValleyN/A776N/AN/A
San Leandro Oyster BedsN/A824N/AN/A
Mills Hall71000132849N/AN/A
Paramount Theatre73000395884N/AN/A
First Unitarian Church of Oakland81000143896N/AN/A
Berkeley City Club77000282908N/AN/A
Peralta Hacienda Site77000285925N/AN/A
University of California, Berkeley Campus82004638946N/AN/A
Croll Building82000960954N/AN/A
Wente Bros WineryN/A957N/AN/A
Site of Blossom Rock Navigation TreesN/A962N/AN/A
Site of the China Clipper Flight DepartureN/A968N/AN/A
Rainbow Trout Specie IdentifiedN/A970N/AN/A
Piedmont WayN/A986N/AN/A
Ukrania, Site of Agapius Honcharenko FarmsteadN/A1025N/AN/A
Pardee Home760004761027N/AN/A
USS HornetN/A1029N/AN/A
Coastguard Lightship WLV-605 – Relief890024621036N/AN/A
Campbell TowerN/AN/APoint of InterestN/A
Memorial To Portuguese ImmigrantsN/AN/APoint of InterestN/A