Mission Viejo ( vee-AY-hoh; 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.