County · code 06001
Alameda CountyCalifornia
Alameda County, California, was created on March 25, 1853, from parts of Contra Costa and Santa Clara counties, with Oakland as its county seat. The county is named after Rancho Arroyo de la Alameda.
- Founded1853
- County seatOakland
- Named forRancho Arroyo de la Alameda, California
- Land area737 sq mi + 84 sq mi water
- Population1,682,353 2020 Census
- Parcels mapped489,646 checked 15 October 2026
Where it is
Alameda on the map of California
California has 58 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Formed in 1853 from Contra Costa County and Santa Clara County
An old deed may name a county that no longer exists, or a boundary that has since moved.
Alameda County was created in 1853 from Contra Costa and Santa Clara counties. In 1874, Alameda gained a small area in San Francisco Bay from San Francisco County, placing all of the Central Pacific Railroad Wharf within Alameda.
- 1853Alameda County created Alameda created from Contra Costa and Santa Clara. · Calif. Stats. 1853, 4th sess., ch. 41/pp. 56-59
- 1874Gained territory Alameda gained small area in San Francisco Bay from San Francisco; placed all of the Central Pacific Railroad Wharf in Alameda. The wharf was removed in 1919. · Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, pp. 168-170; Coy, 62-63
- 1958
- 1971
- 1992Gained territory Alameda gained small area from Contra Costa. Ordinance passed 11 August 1992; effective 1 September 1992. · Minutes of the Board of Supervisors, Alameda County, 11 August 1992, ordinance 92-57
Show all 9 changes
- 1853Alameda County created Alameda created from Contra Costa and Santa Clara. · Calif. Stats. 1853, 4th sess., ch. 41/pp. 56-59
- 1874Gained territory Alameda gained small area in San Francisco Bay from San Francisco; placed all of the Central Pacific Railroad Wharf in Alameda. The wharf was removed in 1919. · Calif. Stats. 1873, 20th sess., Acts Amendatory of the Codes, pp. 168-170; Coy, 62-63
- 1878Changed Boundary between Alameda and San Mateo in San Francisco Bay was adjusted. · Calif. Stats. 1877, 22d sess., Acts Amendatory of the Political Code, ch. 197/p. 71
- 1958
- 1971
- 1992Gained territory Alameda gained small area from Contra Costa. Ordinance passed 11 August 1992; effective 1 September 1992. · Minutes of the Board of Supervisors, Alameda County, 11 August 1992, ordinance 92-57
- 1993Changed Alameda boundaries restated to incorporate 1 September 1992 change (no change). · Calif. Stats. 1993-1994, reg. sess., ch. 1195, sec. 2.5/p. 6853
- 1995Lost territory Alameda lost small area to Contra Costa. · Calif. Stats. 1995, reg. sess., ch. 529, sec. 3 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002
- 1996Boundary clarified Alameda boundary clarified (no change).no change· Calif. Stats. 1996, reg. sess., ch. 400, sec. 4 in Official California Legislative Information, http://www.leginfo.ca.gov/statute.html, 23 September 2002
Land and parcels
What the maps cover in Alameda
Who publishes each layer, how good it is, and when we last checked.
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Parcels Good enough
Lot lines and tax-map numbers for 489,646 parcels from Alameda County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 4 October 2026 · checked 15 October 2026 -
Address points Missing
No public address points layer found for Alameda County yet.
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Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
Alameda by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
Who to ask before you build, dig or sell
Official county pages only. We link to them; we do not copy them, because they change.
Inside a city or town, permits usually come from that city rather than the county.
Zoning and code
GIS and maps
County government
- County government
The official website of Alameda County.
See your own lot on these maps
Open Alameda County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about Alameda County
- When was Alameda County founded?
- Alameda County was founded in 1853, formed from Contra Costa County and Santa Clara County, and named after Rancho Arroyo de la Alameda, California.
- What is the county seat of Alameda County?
- The county seat of Alameda County is Oakland.
- Is there an online parcel map for Alameda County?
- Yes. Alameda County publishes a parcel map of 489,646 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has Alameda County's boundary or name changed?
- Alameda County was created in 1853 from Contra Costa County and Santa Clara County. Since then the Atlas of Historical County Boundaries records 6 later changes, most of them small boundary adjustments, chiefly involving Contra Costa County, San Francisco County and San Mateo County.
- Who issues building permits in Alameda County?
- The county's page on building permits: Permit Portal. Inside a city or town, ask that city first.
- Is my lot in a flood zone?
- We do not have flood maps for Alameda County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby