The County of San Diego, more commonly referred to as San Diego County is the second most populous county in California and the fifth most populous in the United States. It was established in 1850 when California became a U.S. State. The county seat is San Diego which is the second most populous city in California and the eighth most populous city in the United States. San Diego County has more than seventy miles of coastline. North San Diego County is known as North County. It is the most affluent region of the county.

Cities in San Diego County include: