Sierra Vista is a city in Cochise County, Arizona, United States. According to the 2020 Census, the population of the city is 45,308, and is the 27th most populous city in Arizona. The city is part of the Sierra Vista-Douglas Metropolitan Area, with a 2010 population of 131,346. Fort Huachuca, a U.S. Army post, has been incorporated and is located in the northwest part of the city.