Alameda County area

Population and density of Alameda County

The Census Bureau estimates that 1,636,630 people lived in Alameda County on July 1, 2025. That ranks #22 of 3,222 county equivalents nationally and #7 of 58 in California. Since the April 1, 2020 estimates base of 1,682,246, the population has declined by 45,616 (−2.7%), compared with −0.5% for California as a whole.

With 737.5 square miles of land, that is 2,219 people per square mile (857 per km²), placing Alameda County #72 nationally for density and #4 in California. The median county equivalent has 47 people per square mile; the California median is 112. Put another way, there are about 0.288 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Alameda County

14 incorporated places lie at least partly in Alameda County. Together they are home to 1,494,413 people (91.3%); the other 142,217 (8.7%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Oakland city, with 440,838 residents in the county. By land, Fremont city is the largest at 78.1 mi². Among places with at least 1,000 residents in 2020, Emeryville city grew fastest since then (+3.5%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Alameda County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Alameda County is a central county of the San Francisco-Oakland-Fremont, CA Metropolitan Statistical Area, in the Oakland-Fremont-Berkeley, CA metropolitan division. Its 5 county equivalents have 4,630,041 residents on 2,469.8 square miles of land; Alameda County accounts for 29.9% of the land and 35.3% of the residents. By combined land it ranks #133 of 393 metropolitan areas, and #13 by population. It belongs to the San Jose-San Francisco-Oakland, CA Combined Statistical Area.

ZIP codes

53 ZIP Code Tabulation Areas have land in Alameda County; 49 of them have most of their land inside the county, and the others mainly cover neighboring areas.

9450194502945059451494536945389453994541945429454494545945469455094551945529455594560945669456894577945789457994580945869458794588946019460294603946059460694607946089460994610946119461294613946189461994621947029470394704947059470694707947089470994710947209537795391

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Alameda County

Alameda County shares a land border with 4 county equivalents. It has more land than 2 of them. The largest neighbor is San Joaquin County (1,392.3 mi²) and the smallest is San Francisco County (46.7 mi²). Together with its neighbors, Alameda County forms a block of 4,184.4 mi² of land, of which it holds 17.6%.

How big is Alameda County compared with U.S. states?

Alameda County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.4 times as much. California’s county land could hold about 211 areas the size of Alameda County.

Another way to picture it: the same land area would fill a square about 27.2 miles (43.7 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Alameda County?

Alameda County has more land than 2,022 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Alameda County at #1,132 nationally by total area, 68 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.

Its water share is 10.2%, compared with a national county-equivalent median of 1.2% — 9 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Alameda County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.