Map - Mission Viejo, California (Mission Viejo)

Mission Viejo (corruption of Misión Vieja, Spanish for "Old Mission") is a commuter city in the Saddleback Valley in Orange County, California, United States. Mission Viejo is considered one of the largest master-planned communities ever built under a single project in the United States and is rivaled only by Highlands Ranch in size. Its population as of 2020 was 93,653.

Mission Viejo is suburban in nature and culture, and consists of residential properties, offices and businesses. The city is noted for its tree-lined neighborhoods, receiving recognition from the National Arbor Day Foundation. The city's name is a reference to Rancho Mission Viejo, a large Spanish land grant from which the community was founded.

The United States Census Bureau defines an urban area of Orange County cities not part of Los Angeles's urban area with Mission Viejo as the principal city: the Mission Viejo–Lake Forest–Laguna Niguel, CA urban area had a population of 646,843 as of the 2020 census, ranked 65th in the United States.

Rancho Mission Viejo was purchased by Don Juan Forster, an English-born Mexican ranchero. During the Mexican–American War, Forster provided fresh horses to United States military forces which were used on the march of San Diego to invade Los Angeles.

Mission Viejo was a hilly region primarily used as cattle and sheep grazing land, since it was of little use to farmers. This city was one of the last regions of Orange County to be urbanized due to its geologic complexity. In 1960, early developers dismissed most of the land in Mission Viejo as simply "undevelopable".

Donald Bren, an urban planner who later became the president of the Irvine Company, drafted a master plan which placed roads in the valleys and houses on the hills, and contoured to the geography of the area. The plan worked, and by 1980 much of the city of Mission Viejo was completed. During the late 1970s and the 1980s, houses in Mission Viejo were in such high demand that housing tracts often sold out before construction even began on them. The houses and shopping centers in the city are almost uniformly designed in a Spanish mission style, with "adobe"-like stucco walls and barrel-tile roofs. Many point to Mission Viejo as the first and largest manifestation of Bren's obsession with Spanish architecture. Bren's company was also the creator of the developments in Irvine and Newport Beach. The company expanded its operations and went on to build the Lakes project in Tempe, Arizona, Mission Viejo Aurora in Colorado and was the initial master planner of Highlands Ranch, both in the Denver Metropolitan area.

The seal of the city of Mission Viejo was designed and drawn by Carl Glassford, an artist and former resident of the city.