20 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| San Mateo | 1 | 101,680 | 105,658 | -0.65% | 8,380 | 12 | City |
| Daly City | 2 | 99,654 | 104,945 | -0.88% | 13,027 | 8 | City |
| Redwood City | 3 | 82,535 | 83,875 | -0.27% | 4,268 | 19 | City |
| South San Francisco | 4 | 64,038 | 65,903 | -0.48% | 6,958 | 9 | City |
| San Bruno | 5 | 41,177 | 43,750 | -1.03% | 7,502 | 5 | City |
| Pacifica | 6 | 36,313 | 38,541 | -1.01% | 2,886 | 13 | City |
| Menlo Park | 7 | 32,715 | 33,689 | -0.49% | 3,275 | 10 | City |
| Foster City | 8 | 32,117 | 33,737 | -0.83% | 8,481 | 4 | City |
| Burlingame | 9 | 30,688 | 31,279 | -0.32% | 6,986 | 4 | City |
| East Palo Alto | 10 | 28,972 | 29,944 | -0.56% | 11,460 | 3 | City |
| San Carlos | 11 | 28,780 | 30,648 | -1.07% | 5,318 | 5 | City |
| Belmont | 12 | 26,565 | 28,265 | -1.05% | 5,738 | 5 | City |
| Millbrae | 13 | 23,412 | 23,138 | 0.2% | 7,162 | 3 | City |
| Half Moon Bay | 14 | 11,102 | 11,767 | -0.99% | 1,779 | 6 | City |
| Hillsborough | 15 | 11,076 | 11,360 | -0.42% | 1,796 | 6 | Town |
| Atherton | 16 | 6,946 | 7,173 | -0.54% | 1,385 | 5 | Town |
| Woodside | 17 | 5,039 | 5,290 | -0.83% | 439 | 11 | Town |
| Brisbane | 18 | 4,580 | 4,841 | -0.93% | 1,534 | 3 | City |
| Portola Valley | 19 | 4,200 | 4,446 | -0.97% | 462 | 9 | Town |
| Colma | 20 | 1,393 | 1,497 | -1.21% | 737 | 2 | Town |
San Mateo is the largest city in San Mateo County, with a population of 101,680.
Colma is the smallest city in San Mateo County, with a population of 1,393.
There are 20 cities in San Mateo County, California.