| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| San Mateo | 1 | 102,633 | 105,669 | -0.68% | 8,458 | 12 | City |
| Daly City | 2 | 100,332 | 104,806 | -0.92% | 13,115 | 8 | City |
| Redwood City | 3 | 81,821 | 83,889 | -0.43% | 4,232 | 19 | City |
| South San Francisco | 4 | 64,583 | 65,913 | -0.55% | 7,017 | 9 | City |
| San Bruno | 5 | 41,877 | 43,755 | -1.01% | 7,629 | 5 | City |
| Pacifica | 6 | 36,484 | 38,541 | -1.1% | 2,899 | 13 | City |
| Menlo Park | 7 | 32,472 | 33,677 | -0.74% | 3,250 | 10 | City |
| Foster City | 8 | 32,105 | 33,737 | -0.94% | 8,478 | 4 | City |
| Burlingame | 9 | 31,868 | 31,299 | -0.19% | 7,254 | 4 | City |
| San Carlos | 10 | 28,922 | 30,649 | -1.16% | 5,344 | 5 | City |
| East Palo Alto | 11 | 28,625 | 29,959 | -0.86% | 11,323 | 3 | City |
| Belmont | 12 | 28,590 | 28,261 | -0.56% | 6,175 | 5 | City |
| Millbrae | 13 | 22,814 | 23,138 | -0.24% | 6,979 | 3 | City |
| Half Moon Bay | 14 | 11,166 | 11,763 | -1.07% | 1,789 | 6 | City |
| Hillsborough | 15 | 11,149 | 11,351 | -0.51% | 1,808 | 6 | Town |
| Atherton | 16 | 6,909 | 7,163 | -0.73% | 1,377 | 5 | Town |
| Woodside | 17 | 5,140 | 5,297 | -0.79% | 448 | 11 | Town |
| Brisbane | 18 | 4,606 | 4,861 | -1.07% | 1,543 | 3 | City |
| Portola Valley | 19 | 4,249 | 4,445 | -1% | 468 | 9 | Town |
| Colma | 20 | 1,366 | 1,464 | -1.37% | 722 | 2 | Town |
San Mateo is the largest city in San Mateo County, with a population of 102,633.
Colma is the smallest city in San Mateo County, with a population of 1,366.
There are 20 cities in San Mateo County, California.