Claim: San Jose, California has a smaller population than San Diego.

San Diego -LRB- -LSB- ˌsæn_diːˈeɪɡoʊ -RSB- , Spanish for `` Saint Didacus '' ; Spanish : -LSB- san ˈdje.ɣo -RSB- -RRB- is a major city in California , United States . It is in San Diego County , on the coast of the Pacific Ocean in Southern California , approximately 120 mi south of Los Angeles and immediately adjacent to the border with Mexico .   With an estimated population of 1,394,928 as of July 1 , 2015 , San Diego is the eighth-largest city in the United States and second-largest in California . It is part of the San Diego -- Tijuana conurbation , the second-largest transborder agglomeration between the US and a bordering country after Detroit -- Windsor , with a population of 4,922,723 people . San Diego has been called `` the birthplace of California '' . It is known for its mild year-round climate , natural deep-water harbor , extensive beaches , long association with the United States Navy , and recent emergence as a healthcare and biotechnology development center .   Historically home to the Kumeyaay people , San Diego was the first site visited by Europeans on what is now the West Coast of the United States . Upon landing in San Diego Bay in 1542 , Juan Rodríguez Cabrillo claimed the area for Spain , forming the basis for the settlement of Alta California 200 years later . The Presidio and Mission San Diego de Alcalá , founded in 1769 , formed the first European settlement in what is now California . In 1821 , San Diego became part of the newly independent Mexico , which reformed as the First Mexican Republic two years later . In 1850 , California became part of the United States following the Mexican -- American War and the admission of California to the union .   The city is the seat of San Diego County and is the economic center of the region as well as the San Diego -- Tijuana metropolitan area . San Diego 's main economic engines are military and defense-related activities , tourism , international trade , and manufacturing . The presence of the University of California , San Diego -LRB- UCSD -RRB- , with the affiliated UCSD Medical Center , has helped make the area a center of research in biotechnology .