Tucson is a city in and the county seat of Pima County, Arizona, United States, and is home to the University of Arizona. It is the second-largest city in Arizona behind Phoenix, with a population of 542,629 in the 2020 United States census, while the population of the entire Tucson metropolitan statistical area is 1,043,433. The Tucson MSA forms part of the larger Tucson-Nogales combined statistical area. Both Tucson and Phoenix anchor the Arizona Sun Corridor.