San Marcos San Marcos is a city located in the northern portion of San Diego County, California. As of 2006, the city had a total population of 76,725. Outside the San Diego region, it is best known as the home of California State University, San Marcos. San Marcos is known for having some of the best restaurants in North County. Old California Restaurant Row features a large concentration of restaurants offering a variety of cuisines. San Marcos features several golf courses, notably Lake San Marcos, which itself is a recreational venue. Recently, the growth of Cal State San Marcos has led to great opportunities for youth (such as the high-tech sector) are increasingly setting up workshop in the city's robust economy. Finally, San Marcos is home to a large population of retired persons and older adults. There are a variety of businesses offering services to this population.