Oceanside was first settled by the Luiseno, or Payomkawichum. The city lies in the area along the San Luis Rey River that the Luiseno called Tacayme, which held the villages of Qee'ish near the later mission, Wiyooya at the river's mouth, and others at Guajome. Europeans first arrived in 1769 with the Portola expedition. Spanish missionaries under Father Junipero Serra founded Mission San Luis Rey de Francia on the site of the Luiseno village of Keish, and farming and grazing soon changed the landscape.
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After Mexico secularized the missions in 1833, soldiers removed Padre Antonio Peyri, who had led San Luis Rey for 34 years, and Captain Pablo de la Portilla was made administrator. Relations with the Luiseno broke down, and in 1835 they famously refused to work for Portilla.
Andrew Jackson Myers, an emigrant from Illinois, settled in 1882 on the land that became the original Oceanside townsite, and the federal government issued the patent in 1883. Oceanside was incorporated on July 3, 1888, and City Hall now stands on the old Myers homestead. The post office holds Air Mail, an oil-on-canvas mural painted in 1937 by Elsie Seeds under a federal art program.
Sources
Wikipedia: Oceanside, California