| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oakland | 1 | 440,592 | 441,157 | -0.06% | 7,873 | 56 | City |
| Fremont | 2 | 225,515 | 230,446 | -0.41% | 2,887 | 78 | City |
| Hayward | 3 | 155,727 | 162,692 | -0.88% | 3,399 | 46 | City |
| Berkeley | 4 | 121,041 | 124,142 | -0.71% | 11,603 | 10 | City |
| San Leandro | 5 | 84,146 | 90,731 | -1.41% | 6,316 | 13 | City |
| Livermore | 6 | 82,469 | 87,876 | -1.18% | 3,104 | 27 | City |
| Alameda | 7 | 76,653 | 78,115 | -0.29% | 7,371 | 10 | City |
| Pleasanton | 8 | 73,402 | 79,673 | -1.55% | 3,041 | 24 | City |
| Dublin | 9 | 71,128 | 72,182 | -0.66% | 4,671 | 15 | City |
| Union City | 10 | 64,223 | 69,932 | -1.62% | 3,311 | 19 | City |
| Newark | 11 | 47,902 | 47,520 | 0.01% | 3,441 | 14 | City |
| Mountain House | 12 | 28,669 | 24,560 | 4.32% | 3,855 | 7 | City |
| Mountain House | 13 | 28,669 | 24,560 | 13.25% | 3,855 | 7 | City |
| Mountain House | 14 | 25,440 | 24,560 | -7.43% | 3,421 | 7 | City |
| Mountain House | 15 | 25,440 | 24,560 | 0.49% | 3,421 | 7 | City |
| Albany | 16 | 18,944 | 20,206 | -1.31% | 10,583 | 2 | City |
| Emeryville | 17 | 13,378 | 12,816 | 0.96% | 10,509 | 1 | City |
| Piedmont | 18 | 10,507 | 11,242 | -1.27% | 6,181 | 2 | City |
Oakland is the largest city in Alameda County, with a population of 440,592.
Piedmont is the smallest city in Alameda County, with a population of 10,507.
There are 18 cities in Alameda County, California.