[2] Rancho Simi was the earliest Spanish colonial land grant within Ventura and Santa Barbara Counties.

[3] At 113,000 acres, Rancho Simi was one of the state's largest land grants.

The home remained in the Strathearn family until 1969, when the dwelling and 5.85 acres (2.37 ha) of surrounding land were donated to the Simi Valley Recreation and Park District.

In addition to the Simi Adobe–Strathearn House, there are various historic buildings and structures that have been moved from their original site to the park, including the 1924 Montgomery children's playhouse, the 1902 St. Rose of Lima Catholic Church, the original Simi Valley Library, a Colony House built in 1888,[7][8] the Banaga Barber Shop, the Currier pitting shed, and two barns with farm tools and equipment.

The site is home to the Simi Valley Historical Society which seeks to acquire, preserve, maintain, identify and mark historical buildings, sites and landmarks; to collect artifacts of historical significance; to provide and maintain a sanctuary for such artifacts; to provide for the public a reservoir of historical information; to encourage and continue research in the history of the area.