In 1842, after California had passed from Spanish to Mexican rule, Jose' Antonio Estudillo was granted the 35,500-acre Rancho San Jacinto Viejo (Old San Jacinto), which took in most of the Valley.
Members of his family received two other nearby grants, giving the Estudillo family control over some 110,000 acres in the area. The Estudillos ran cattle on the land. Jose' Estudillo died in 1852, but his family continued to own most of the Valley until the early 1880's. Two of his sons built two-story brick mansions in 1885 - 1886. The oldest, built by Franciso Estudillo (1844 - 1921) in 1885, is located at Main and Seventh Streets in San Jacinto.
The Estudillo Mansion is currently owned by the City of San Jacinto. The City successfully completed the interior and exterior Estudillo Mansion Restoration project in 2009.
It has been named the most significant historical building in the San Jacinto Valley and is one of the most significant in all of Riverside County.
On January 2, 2002, the City of San Jacinto announced the placement of the Estudillo Mansion and the Francisco Heritage Park on the California Register of Historic Resources. This is only the third Riverside County site to receive this honor.
Francisco Estudillo was San Jacinto's first postmaster and was also appointed Mission Indian Agent for the Federal Government, responsible for 32 reservations in southern and central California. He was elected to the local school board and in 1890 was elected San Jacinto's second mayor, serving until 1892. Many members of the Estudillo family married other early famous California people such as those of the Pico family. There are many descendants and two reunions have been held at the mansion.
After passing through many owners, the mansion was purchased by the County of Riverside in 1992. It had been severely damaged by the Landers-Big Bear earthquakes on June 28, 1992. The County turned ownership over to the City of San Jacinto in 1998.