| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Concord | 1 | 122,839 | 125,282 | -0.34% | 4,019 | 31 | City |
| Antioch | 2 | 119,688 | 115,388 | 0.61% | 4,103 | 29 | City |
| Richmond | 3 | 114,604 | 116,108 | -0.22% | 3,815 | 30 | City |
| San Ramon | 4 | 86,091 | 86,500 | -0.14% | 4,292 | 20 | City |
| Pittsburg | 5 | 77,709 | 76,356 | 0.22% | 4,168 | 19 | City |
| Walnut Creek | 6 | 70,027 | 70,223 | 0.02% | 3,544 | 20 | City |
| Brentwood | 7 | 67,037 | 64,457 | 0.65% | 4,510 | 15 | City |
| Oakley | 8 | 48,449 | 43,484 | 1.82% | 3,054 | 16 | City |
| Danville | 9 | 43,251 | 43,565 | -0.12% | 2,392 | 18 | Town |
| Martinez | 10 | 36,787 | 37,171 | -0.17% | 2,910 | 13 | City |
| Pleasant Hill | 11 | 33,893 | 34,579 | -0.36% | 4,791 | 7 | City |
| San Pablo | 12 | 31,547 | 32,126 | -0.41% | 12,022 | 3 | City |
| Hercules | 13 | 26,407 | 26,118 | 0.31% | 4,118 | 6 | City |
| El Cerrito | 14 | 26,175 | 25,969 | 0.21% | 7,128 | 4 | City |
| Lafayette | 15 | 25,294 | 25,394 | -0.08% | 1,684 | 15 | City |
| Orinda | 16 | 19,511 | 19,513 | 0.02% | 1,518 | 13 | City |
| Pinole | 17 | 18,448 | 18,999 | -0.51% | 3,614 | 5 | City |
| Moraga | 18 | 16,264 | 16,875 | -0.36% | 1,719 | 9 | Town |
| Clayton | 19 | 10,798 | 11,060 | -0.41% | 2,812 | 4 | City |
Concord is the largest city in Contra Costa County, with a population of 122,839.
Clayton is the smallest city in Contra Costa County, with a population of 10,798.
There are 19 cities in Contra Costa County, California.