San Marcos is a city in the North County region of San Diego County, California. As of the 2020 census, the city's population was 94,833. It is the site of California State University San Marcos and Palomar College. The city is bordered by Escondido to the east, Encinitas to the southwest, Carlsbad to the west, and Vista to the northwest. Lake San Marcos is an enclave, or county island, within the southwestern part of the city and its sphere of influence but is an unincorporated community.

North County is a region in the northern area of San Diego County, California. It is the second-most populous region in the county, with an estimated population of 869,322. North County is well known for its affluence, especially in Encinitas, Carlsbad, Del Mar, Rancho Santa Fe, Poway and Solana Beach, where house prices range, on average, above $1,000,000. Cities along the 78 freeway have more mixed incomes.