Created by virtue of P.D. 1778 on January 15, 1981, the Don Mariano Marcos Memorial State University (DMMMSU) is a merger of five former schools of La Union as follows:
- Don Mariano Marcos Memorial State College (formerly known as the Don Mariano Marcos Memorial College of Agriculture and the La Union Agricultural School), founded on June 18, 1960; located in Barangay Sapilang, Bacnotan, La Union;
- La Union School of Arts and Trades (located in San Fernando, La Union; founded in 1907);
- Southern Ilocos Polytechnic State College (composed of Southern LA Union National High School in Agoo, Sto. Tomas College of Fisheries, and Rosario National Agricultural School; established on July 28, 1977);
- Community College of La Union (located in San Fernando; founded in 1968); and
- Sapilang Elementary School (located in Barangay Sapilang, Bacnotan, La Union; founded in June 1969)
The late Dr. Bienvenido P. Agpaoa became the first University President until October 1988. He was succeeded in February 1989 by Dr. Manuel T. Corpus, former president of the Cagayan State University.
Atty. Benjamin P. Sapitula is currently the DMMMSU President.
At present, the University is sprawled on a 1,120 hectares, cozily splintered in its three major campuses: North La Union Campus (Bacnotan and Balaoan towns), Mid La Union Campus (San Fernando) and the South La Union Campus (Agoo, Sto. Tomas, and Rosario towns).