The Spanish word alameda means either "a grove of poplars...or a tree lined street".

In 1856, it was moved to San Leandro, where the county courthouse was destroyed by the devastating 1868 quake on the Hayward Fault.

Much of what is now an intensively urban region was initially 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 to multiple city centers and suburbs, is shared with the adjacent and closely associated Contra Costa County.

In addition it is the local government for all unincorporated areas, and provides services such as law enforcement to some incorporated cities under a contract arrangement.

The current Sheriff is Yesenia Sanchez, who was elected in 2022, succeeding Greg Ahern, who had served in the post for 16 years.

In 2009, Nancy E. O'Malley was appointed Alameda County district attorney after Tom Orloff retired.

[14] The Alameda County Fire Department (ACFD)[15] was formed on July 1, 1993, as a dependent district, with the Board of Supervisors as its governing body.

1993 brought in the Castro Valley and Eden Consolidated FD, and the County Fire Patrol.

San Leandro joined in 1995, Dublin in 1997, Lawrence Berkeley National Laboratory in 2002, Lawrence Livermore National Laboratory in 2007, The Alameda County Regional Emergency Communications Center in 2008, and Newark and Union City in 2010.

Most major criminal trials and complex civil cases are heard at this location or in courtrooms within the County Administration Building across the street.

[19] On November 4, 2008, Alameda County voted 61.92% against Proposition 8, which won statewide, and which amended the California Constitution to ban same-sex marriage.

The crest of the Berkeley Hills forms part of the northeastern boundary and reaches into the center of the county.

A coastal plain several miles wide lines the bay; and is Oakland's most populous region.

The areas near the Bay itself have a maritime warm-summer Mediterranean climate, whereas behind the mountains, summers are significantly warmer.

The racial makeup of Alameda County was 649,122 (43.0%) White, 190,451 (12.6%) African American, 9,799 (0.6%) Native American, 394,560 (26.1%) Asian (9.7% Chinese, 5.5% Filipino, 4.8% Indian, 2.0% Vietnamese, 1.2% Korean, 0.8% Japanese, 2.2% Other Asian), 12,802 (0.8%) Pacific Islander, 162,540 (10.8%) from other races, and 90,997 (6.0%) from two or more races.

The remainder of Hispanics self-identify as Other Race (49.2%), Multiracial (8.7%), American Indian and Alaskan Native (1.9%), Black (1.5%), Asian (0.9%), and Hawaiian and Pacific Islander (0.2%).

If treated as a category separate from race, Hispanics are the third largest minority group in Alameda County.

[56] The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.

The ACOE also services three community college districts with a total enrollment of approximately 55,000 students.

The cities of Alameda, Berkeley, Hayward, Livermore, Oakland, San Leandro, and Pleasanton have their own library systems.

Its fifteen appointed members act in an advisory capacity to the board of supervisors, in promoting the arts.

Attractions include horse racing, carnival rides, 4-H exhibits, and live bands.

Eastshore State Park is located partially along the bay shore of northern Alameda County.

Alameda County has eight National Historic Landmarks: The Abbey, Joaquin Miller House, First Church of Christ, Scientist, USS Hornet (CVS-12) (aircraft carrier), Lake Merritt Wild Duck Refuge, Lightship WAL-605, Relief, Paramount Theatre, Potomac (Presidential yacht), and Room 307, Gilman Hall, University of California.