19 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Concord | 1 | 123,699 | 125,284 | -0.26% | 4,047 | 31 | City |
| Antioch | 2 | 119,220 | 115,382 | 0.65% | 4,087 | 29 | City |
| Richmond | 3 | 115,147 | 116,177 | -0.18% | 3,833 | 30 | City |
| San Ramon | 4 | 85,808 | 86,385 | -0.14% | 4,278 | 20 | City |
| Pittsburg | 5 | 77,325 | 76,355 | 0.25% | 4,148 | 19 | City |
| Walnut Creek | 6 | 70,966 | 70,218 | 0.21% | 3,591 | 20 | City |
| Brentwood | 7 | 66,744 | 64,454 | 0.69% | 4,490 | 15 | City |
| Oakley | 8 | 48,077 | 43,482 | 1.95% | 3,030 | 16 | City |
| Danville | 9 | 43,371 | 43,563 | -0.09% | 2,399 | 18 | Town |
| Martinez | 10 | 36,960 | 37,187 | -0.12% | 2,923 | 13 | City |
| Pleasant Hill | 11 | 34,064 | 34,589 | -0.31% | 4,815 | 7 | City |
| San Pablo | 12 | 31,427 | 32,099 | -0.43% | 11,977 | 3 | City |
| Hercules | 13 | 26,594 | 26,117 | 0.36% | 4,147 | 6 | City |
| El Cerrito | 14 | 26,525 | 25,944 | 0.44% | 7,224 | 4 | City |
| Lafayette | 15 | 25,367 | 25,386 | -0.02% | 1,688 | 15 | City |
| Orinda | 16 | 19,588 | 19,512 | 0.08% | 1,524 | 13 | City |
| Pinole | 17 | 18,578 | 19,003 | -0.46% | 3,640 | 5 | City |
| Moraga | 18 | 16,651 | 16,886 | -0.28% | 1,760 | 9 | Town |
| Clayton | 19 | 10,901 | 11,061 | -0.29% | 2,839 | 4 | City |
Concord is the largest city in Contra Costa County, with a population of 123,699.
Clayton is the smallest city in Contra Costa County, with a population of 10,901.
There are 19 cities in Contra Costa County, California.