San Marcos initially started to grow in 1956 when the first water from the Colorado River arrived.  After the arrival of water, several small businesses started and the population rapidly increased to 2500.  Then in 1950, the first dirt was turned for the construction of Highway 78 and San Marcosÿ first high school was completed in June 1961.  The City became incorporated on January 28, 1963.  Through the 1960s the City grew by a few thousand new residents, but in the 1970s, San Marcos was flourishing as the third fastest growing city in the state with a population of 17,479 by 1980.  During the 1980s, San Marcos almost doubled its population to 33,800. Growth has continued to boom in San Marcos, and the present population of the City is at 67,426.

In 1989, Cal State University San Marcos opened. This University has brought in an influx of young students, as well as academics of every race, religion, ethnicity, and creed. Cal State San Marcos is a rapidly growing, modern campus of new buildings, the latest computer technology, cutting-edge science labs, and has created a sense of excitement about the future of San Marcos. Palomar Community College is also in San Marcos. With the University there has been a growth, upscale developments, and influx of large retailers.

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.