Tucson is a city in and the county seat of Pima County, Arizona, United States, and is home to the University of Arizona. The 2010 United States Census put the population at 520,116, while the 2015 estimated population of the entire Tucson metropolitan statistical area was 980,263. The Tucson MSA forms part of the larger Tucson-Nogales combined statistical area, with a total population of 1,010,025 as of the 2010 Census. 

Tucson is the second most-populated city in Arizona behind Phoenix, both of which anchor the Arizona Sun Corridor. The city is 108 miles southeast of Phoenix and 60 miles north of the U.S.–Mexico border. Tucson is the 33rd largest city and the 58th largest metropolitan area in the United States (2014).

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 include Casas Adobes, Catalina Foothills, Flowing Wells, Midvale Park, Tanque Verde, Tortolita, and Vail. Towns outside the Tucson metro area include Benson to the southeast, Catalina and Oracle to the north, and Green Valley to the south.

Tucson was founded as a military fort by the Spanish when Hugo O'Conor authorized the construction of Presidio San Agustín del Tucsón in 1775. It was included in the state of Sonora after Mexico gained independence from the Spanish Empire in 1821. In 1853, the United States acquired a 29,670-square-mile region of present-day southern Arizona and southwestern New Mexico from Mexico under the Gadsden Purchase. Tucson served as the capital of the Arizona Territory from 1867-1877. Tucson was Arizona's largest city by population during the territorial period and early statehood until it was surpassed by Phoenix by 1920. Nevertheless, population growth remained strong during the late 20th century.