The founding of San Buenaventura Mission traces to the decision on Palm Sunday, March 30, 1749 by the Franciscan priest Junipero Serra to journey to the New World as a missionary to the native peoples. (Padre Serra was canonized a Saint by Pope Francis on September 23, 2015.)

Thirty-three years and one day later Saint Junipero Serra raised the Cross at "la playa de la canal de Santa Barbara" (the beach of the Santa Barbara Channel) on Easter Morning, March 31, 1782. Assisted by Padre Pedro Benito Cambon, he celebrated a High Mass, preached on the Resurrection, and dedicated a Mission to San Buenaventura (St. Bonaventure). It had been planned as the third in the chain of twenty-one Missions founded by Padre Serra but was destined to be the ninth and last founded during his lifetime, and one of six he personally dedicated.