Tucson is the county seat of and the most populated city in Pima County, Arizona, United States. It is the second-most populous city in Arizona with a population of 542,630 at the 2020 census, behind the capital city, Phoenix, while the Tucson metropolitan statistical area has an estimated 1.08 million residents and is the 52nd-largest metropolitan area in the United States. Tucson and Phoenix anchor the Arizona Sun Corridor. The city is 108 miles southeast of Phoenix and 60 mi (100 km) north of the United States–Mexico border. It is home to the University of Arizona.