The County of San Diego is the southernmost county in California. It is also the southwesternmost county in the Mainland United States. As of 2025, San Diego County has a population of 3,298,634 residents, making it the second most populated county in California behind only Los Angeles County. The county seat is the city of San Diego, which is also the second largest city in the state, home to 1.4 million people.
Cities in San Diego County
| City Name | Year Founded | Population in 2020 Census |
| San Diego | 1769 | 1,386,932 |
| Chula Vista | 1911 | 275,487 |
| Oceanside | 1888 | 174,068 |
| Escondido | 1888 | 151,038 |
| Carlsbad | 1952 | 114,746 |
| El Cajon | 1912 | 106,215 |
| Vista | 1963 | 98,381 |
| San Marcos | 1963 | 94,833 |
| Encinitas | 1986 | 62,007 |
| La Mesa | 1912 | 61,121 |
| Santee | 1980 | 60,037 |
| National City | 1887 | 56,173 |
| Poway | 1980 | 48,841 |
| Lemon Grove | 1977 | 27,627 |
| Imperial Beach | 1956 | 26,137 |
| Coronado | 1890 | 20,192 |
| Solana Beach | 1986 | 12,941 |
| Del Mar | 1959 | 3,954 |
Notable People from San Diego County
- Michael McGrath, son of Joe McGrath (born in San Diego)
Famous Attractions
- LEGOLAND California Resort, amusement park theme the LEGOs (Carlsbad)
- Maritime Museum of San Diego, home of the Star of India ship (San Diego)
- Petco Park, home of the San Diego Padres baseball team (San Diego)