Originally inhabited by Native Americans, the first European explorers arrived in 1769. Spanish missionaries under Father Junipero Serra foundedMission San Luis Rey de Francia on a former site of a Luiseño Indian village on the banks of the San Luis Rey River. In the early 19th century, the introduction of farming and grazing changed the landscape of what would become Oceanside. The area—like all of California—was under Spanish, then in 1821 under Mexican rule, and conquered by the U.S. in 1848.
In the late 1850s, Andrew Jackson Myers lived in San Joaquin County. A native of LaSalle County, Illinois, he returned in the late 1880s and lived inSan Luis Rey. In 1882 Myers moved on the land that was the original town site for Oceanside. A patent for the land was issued in 1883 by the federal government. It was incorporated on July 3, 1888. The city hall as of the early 21st century stands on the former Myers homestead.
In the 20th century, Oceanside was a beach town devoted to activities on a 6-mile (9.7 km) stretch of beaches. Residential areas like downtown (built in the 1890s), South Oceanside (built in the 1920s and 1930s), and developments east of Interstate 5 (built after World War II) are preserved and remodeled when these houses are considered to have historical value. Since the establishment of Marine Corps Base Camp Pendletonin 1942, Oceanside has been home to U.S. armed forces personnel, and the wartime industry of WWII and the 1950s had an ammunition manufacturing facility in the city.
In 1970, the Census Bureau reported city’s population as 91.0% white, 5.1% black and 1.7% Asian.After 1970, the main focus of Oceanside was suburban development and a choice for newcomers to move into then relatively affordable housing. Oceanside continues to be known for the value and appreciation as a vacation home market.