In 1833, with five other male citizens, Osuna urged the governor to establish a pueblo government for San Diego, to replace 60-some years of military rule.
Lt. Santiago Argüello, the last Commandant of San Diego Presidio gave Osuna his staff of office, symbolizing the transfer of government from the military to civilian self-rule.
Juan María Osuna's adobe, overlooking the San Dieguito River Valley, has been restored and is part of The Rancho Santa Fe Homeowners Association.
Osuna died 1851, and is buried in El Campo Santo Catholic Cemetery in Old Town, San Diego.
A modern headstone reads "Juan Maria Osuna Died 1851 First Alcalde Of San Diego".