22 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oakland | 1 | 433,544 | 440,943 | -0.34% | 7,747 | 55.96 | City |
| Fremont | 2 | 223,393 | 230,430 | -0.63% | 2,860 | 78.10 | City |
| Hayward | 3 | 151,014 | 162,666 | -1.52% | 3,296 | 45.82 | City |
| Berkeley | 4 | 115,466 | 124,205 | -1.49% | 11,068 | 10.43 | City |
| San Leandro | 5 | 82,490 | 90,724 | -1.96% | 6,192 | 13.32 | City |
| Livermore | 6 | 79,596 | 87,875 | -2.04% | 2,996 | 26.57 | City |
| Alameda | 7 | 73,515 | 78,109 | -1.23% | 7,069 | 10.40 | City |
| Pleasanton | 8 | 71,311 | 79,665 | -2.29% | 2,954 | 24.14 | City |
| Dublin | 9 | 67,006 | 72,311 | -1.56% | 4,400 | 15.23 | City |
| Castro Valley | 10 | 66,458 | 64,392 | 0.51% | 3,945 | 16.85 | CDP |
| Union City | 11 | 62,405 | 69,927 | -2.35% | 3,217 | 19.40 | City |
| Newark | 12 | 46,537 | 47,517 | -0.42% | 3,343 | 13.92 | City |
| San Lorenzo | 13 | 31,336 | 30,117 | 1.71% | 10,288 | 3.05 | CDP |
| Mountain House | 14 | 27,069 | 21,387 | 4.48% | 5,939 | 4.56 | CDP |
| Ashland | 15 | 23,474 | 23,566 | 0.45% | 12,737 | 1.84 | CDP |
| Albany | 16 | 18,345 | 20,225 | -2.01% | 10,249 | 1.79 | City |
| Cherryland | 17 | 15,692 | 15,976 | 0.41% | 13,153 | 1.19 | CDP |
| Emeryville | 18 | 12,608 | 12,918 | -0.49% | 9,904 | 1.27 | City |
| Fairview | 19 | 10,728 | 10,834 | 0.45% | 3,607 | 2.97 | CDP |
| Piedmont | 20 | 10,219 | 11,258 | -1.99% | 6,011 | 1.70 | City |
| Kensington | 21 | 5,367 | 5,171 | 0.36% | 5,567 | 0.96 | CDP |
| Sunol | 22 | 922 | 835 | 0.11% | 33 | 28.26 | CDP |
Oakland is the largest city in Alameda County, with a population of 433,544.
Sunol is the smallest city in Alameda County.
There are 22 cities in Alameda County, California.