Lake San Marcos is a unincorporated community in the North County region of the San Diego metropolitan area. For statistical purposes, the United States Census Bureau has defined the community as a census-designated place (CDP). Surrounded by the city of San Marcos, the county-governed area receives certain services from the city.

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.