Aliso Viejo is a city in Orange County, California, United States. As of the 2000 census, Aliso Viejo population was 40,166. Aliso Viejo became Orange County's 34th city on July 1, 2001, and has been the only city in Orange County to incorporate since 2000. It borders the cities of Laguna Beach, Laguna Hills, Laguna Niguel, and Laguna Woods.

The city of Aliso Viejo has played an active role as a city against illegal immigration. The Minutemen Project founder, Jim Gilchrist, is from the city and largely ignited the citywide support for his causes to control and punish those who have come to America illegaly.