Tucson (; O'odham: Cuk Ṣon; Spanish: Tucsón) 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 U.S. Tucson and Phoenix anchor the Arizona Sun Corridor. The city is 108 miles (174 km) southeast of Phoenix and 60 mi (100 km) north of the United States–Mexico border. It is home to the University of Arizona.
Major incorporated suburbs of Tucson include Oro Valley and Marana northwest of the city, Sahuarita south of the city, and South Tucson in an enclave south of downtown. Communities in the vicinity of Tucson (some within or overlapping the city limits) include Casas Adobes, Catalina Foothills, Flowing Wells, Midvale Park, Tanque Verde, Tortolita, and Vail. Towns outside the Tucson metropolitan area include Three Points, Benson to the southeast, Catalina and Oracle to the north, and Green Valley to the south.