California State University San Marcos (also CSUSM or Cal State San Marcos) is a public, coeducational university and one of the 23 general campuses of the California State University system. located in San Marcos, California, a suburban town in north San Diego County. It was founded in 1989 as the 20th CSU campus and was the first after nearly 30 years. The first class was admitted in 1990.