Originally an Indian rancheria, Rancho Santa Fe passed through several hands before becoming a residential community. In 1831, the Spanish Governor Manuel Victoria provisionally granted the 8,824 acres to Lebrado Silva. Juan Maria Osuna, the alcalde of San Diego helped to overthrow Victoria and took possession of the land grant in 1836. Osuna allowed Silva and his family to continue living on the property in an older adobe.

As alcalde, Osuna was an important figure in both the social and political life of San Diego. He also had the power to approve petitions for land, and naturally he approved his own petition for the San Dieguito land. He received a provisional grant in 1840 and 1841, and finally in 1845, Governor Pio Pico gave him full title.

While Osuna preferred to reside in San Diego, he built he and his wife an adobe home on the ranch. He left the duties of managing the property to his son, Leandro, to whom he gave one the the existing adobes on the ranch. Although a fine alcalde, Osuna was also a gambling man, and he lost some of the land to pay off bad debts.

Upon his father's death in 1851, Leandro took possession of the ranch. A veteran of the Battle of San Pasqual in 1846, Leandro was a man of erratic temperament. His cruel treatment of the Indians led to his demise in 1859. Tired of being treated poorly, the Indians poisoned Leandro and then told him of his impending agony. Rather than face a slow, painful death, Leandro committed suicide.

Julio Osuna, Leandro's son then assumed control of the ranch. The Osuna family continued to reside on the ranch for many years, but slowly financial problems forced him to sell a majority of the land grant acreage. By 1906, the Osuna family retained only 200 acres of the once grand rancho.