Alameda County, California

Alameda is a county in California, United States, on the eastern shore of San Francisco Bay directly across the water from the city of San Francisco. It had a population of 1,682,353 at the 2020 census, an estimated 1,636,630 by 2025, and covers 739 square miles (1,914 km2) of land centred near 37°39′N 121°53′W.

Oakland is the county seat and its largest city; its postal code is 94612. The county holds 14 incorporated cities and 6 unincorporated communities, and it runs on Pacific time. Its FIPS code is 06001.

Towns & Villages in Alameda County

Alameda County has 20 named places: 14 incorporated cities, from Oakland (389,397 people) down to Piedmont (10,640), and 6 unincorporated communities recognized by the Census Bureau as CDPs, from Castro Valley (61,388) down to Sunol (913). California has no civil townships, so the table below omits that column.

All 20 places above carry a 2020 census count — the most recent year with a verified figure for every place, incorporated and unincorporated alike. One naming note: Oakland, California, the county seat here, is a different place from Oakland County, Michigan, a Detroit-suburb county of the same name with its own page on this site — the two share nothing but a name.

ZIP Codes

• 94612 — Oakland (downtown/civic center; the city carries dozens more ZIPs citywide)
• 94536 — Fremont (Centerville district; also serves the rest of Fremont’s 94538, 94539 and 94555)
• 94541 — Hayward (also serves unincorporated Cherryland)
• 94704 — Berkeley (also serves UC Berkeley’s 94720)
• 94577 — San Leandro
• 94550 — Livermore
• 94566 — Pleasanton
• 94587 — Union City
• 94501 — Alameda
• 94568 — Dublin
• 94546 — Castro Valley (also 94552)
• 94560 — Newark
• 94580 — San Lorenzo
• 94578 — Ashland (shared with adjoining San Leandro addresses)
• 94706 — Albany
• 94611 — Piedmont (shared with adjoining Oakland addresses)
• 94608 — Emeryville
• 94586 — Sunol

Fairview has no ZIP code of its own; mail there is addressed under neighboring Hayward or San Leandro codes because the community was never assigned a dedicated post office.

Geography

Alameda County spans San Francisco Bay’s eastern shore and rises east into the Diablo Range, with the bayside cities on flat fill and reclaimed marsh and the inland cities — Livermore, Pleasanton, Dublin — sitting in the Livermore Valley behind the Berkeley and Oakland hills. Lake Chabot and Lake Del Valle are the largest bodies of fresh water; San Francisco Bay itself forms the entire western edge. The county borders Contra Costa County to the north, San Joaquin County to the east, Stanislaus County briefly at its southeastern corner, and Santa Clara County to the south. San Francisco County lies directly across the bay to the west, reachable by bridge and BART tube rather than by road.

Demographics

Alameda County counted 1,682,353 residents at the 2020 census and an estimated 1,636,630 as of 2025, a decline driven mostly by the Bay Area’s post-2020 cost-of-living outmigration. Oakland and Fremont are its two largest communities. Median household income was $129,367 in 2024, well above California’s statewide median of roughly $96,000. Population density is about 2,277 people per square mile of land, concentrated along the I-880 and I-580 corridors and thinning sharply east of the Dublin/Pleasanton hills.

Economy & Local Life

Professional, scientific and technical services employ the most workers in the county at roughly 147,600, reflecting the East Bay’s biotech and software cluster around Emeryville, Berkeley and Fremont — Fremont in particular anchors a cluster of electric-vehicle and clean-tech manufacturers. Health care and social assistance employs about 111,800, and manufacturing about 86,800, split between Fremont’s factory floor and Oakland’s port-adjacent logistics firms. The Port of Oakland is the county’s largest single freight employer. UC Berkeley anchors the county’s academic institutions alongside CSU East Bay in Hayward. The Alameda County Fair, held each summer in Pleasanton, is the county’s largest annual event.

History

Alameda County was organized on March 25, 1853, carved from parts of Santa Clara and Contra Costa counties, and named for the Arroyo de la Alameda — Spanish for “poplar grove,” describing the tree-lined creek that once ran through what is now the city of Alameda. The 1868 Hayward earthquake destroyed the original courthouse in San Leandro, then the county seat, and the seat moved briefly to Brooklyn (since annexed into Oakland) before settling permanently in Oakland in 1875. The county’s Spanish and Mexican-era ranchos gave way in the 1850s to wheat farming and orchards, and again in the twentieth century to shipbuilding, canning and, after World War II, to the manufacturing and technology industries that still define its economy.

Getting There

Interstate 880 runs the length of the bayside cities from Oakland to Fremont; Interstate 580 crosses the county east-west through Oakland, Castro Valley and Livermore before continuing into San Joaquin County over the Altamont Pass; Interstate 680 runs north-south through Pleasanton, Dublin and Fremont, and Interstate 238 connects the two Interstates near San Leandro.

• San Francisco — 12 miles west (across the Bay Bridge or BART)
• San Jose — 20 miles south
• Sacramento — 75 miles northeast
• Stockton — 45 miles east

Oakland International Airport is the county’s own commercial airport; San Francisco International Airport sits just across the bay in neighboring San Mateo County. Amtrak’s Capitol Corridor serves the county at Berkeley, Emeryville, Fremont and Hayward stations, and BART’s five lines connect every major city in the county to San Francisco and beyond.

Frequently Asked Questions

Where is Alameda County?
It sits on the eastern shore of San Francisco Bay in Northern California, directly across the water from the city of San Francisco.

What is the population of Alameda County?
It had a population of 1,682,353 at the 2020 census, estimated at 1,636,630 as of 2025.

How big is Alameda County?
739 square miles (1,914 km2) of land, plus 82 square miles of bay water.

What is the county seat of Alameda County?
Oakland, California — also the county’s largest city.

How many towns and cities are in Alameda County?
14 incorporated cities and 6 unincorporated communities recognized as CDPs, 20 places in all.

What ZIP codes are in Alameda County?
Roughly 60 ZIP codes in total; principal ones include 94612 (Oakland), 94536 (Fremont), 94541 (Hayward) and 94704 (Berkeley).

Is Oakland, California the same as Oakland County, Michigan?
No. Oakland, California is Alameda County’s seat and largest city; Oakland County, Michigan is an unrelated Detroit-suburb county roughly 2,300 miles away, and shares only the name.

More counties in this state: Towns and villages in California.