Rancho Mission Viejo (Spanish: Rancho Misión Vieja, meaning “Old Mission Ranch”) is an swift 23,000 acres (9,300 ha) ranch and farm, habitat reserve, residential community, and census-designated place in South Orange County, California. Rancho Mission Viejo originated as a series of land grants to John Forster in 1845. The remaining part of Rancho Mission Viejo consists of a nearly 17,000-acre (6,900 ha) nature reserve (The Reserve at Rancho Mission Viejo) and combination residential communities slated to way in in phases in the company of 2010 and 2030. As of the 2020 census, it had a population of 10,378.

Prior to the founding of the ranch, the land was the site of Acjachemen village of Piwiva. The ranch was acknowledged in 1845 as soon as John (Don Juan) Forster acquired Rancho La Paz and Mission San Juan Capistrano. Forster other these properties to Rancho Trabuco, which he had purchased in 1843. Forster’s brother-in-law was Pío Pico, governor of then-Mexican-held California. In 1864, Forster supplementary Rancho Santa Margarita y Las Flores to his holdings, which later totaled roughly 200,000 acres (81,000 ha), making him one of the largest landowners in the state.

After Forster died in 1882, Irish immigrants Richard O’Neill Sr. and James Flood acquired the ranch, taking equal ownership of the Rancho Santa Margarita y las Flores, Rancho Mission Viejo and Rancho Trabuco lands. Flood provided the keep to purchase the ranches; O’Neill, offering his skills as a cattleman as sweat equity, agreed to work out his half as resident manager. Under O’Neill, the cattle herd was expanded, the home was improved, row crops were introduced, and the ranch became Orange County’s largest producer of wheat.

In 1907, James L. Flood, son of the indigenous owner, made good upon his late father’s conformity and conveyed an undivided half amalgamation to O’Neill Sr. Four months later, declining health caused O’Neill to attainment his assimilation to his son, Jerome. In 1923, the sons of Flood and O’Neill consolidated their partnership afterward the Santa Margarita Company. Shortly thereafter, both men died.