Rancho Simi, also known as Rancho San José de Nuestra Señora de Altagracia y Simí, was a 113,009-acre (457 km2) Spanish land grant in what is now eastern Ventura and western Los Angeles counties granted in 1795 to Santiago Pico, founder of the Pico family of California. After Santiago Pico's death in 1815, the Rancho was regranted to Santiago's sons Javier Pico and his two brothers, Patricio Pico and Miguel Pico by Diego de Borica. The name derives from Shimiji, the name of a Chumash village in the Simi Valley for thousands of years before the Spanish arrival.

Ventura County is a county located in the southern part of the U.S. state of California. As of the 2020 census, the population was 843,843. The largest city is Oxnard, and the county seat is the city of Ventura.