Sister cities of Tucson, Arizona

Tucson (/ˈtuːsɒn/ TOO-son) is a city in and the county seat of Pima County, Arizona, United States, and home to the University of Arizona. The 2010 United States Census puts the city's population at 520,116, while the 2012 estimated population of the entire Tucson metropolitan area was 992,394. The Tucson MSA forms part of the larger Tucson-Nogales combined statistical area, with a total population of 980,263 as of the 2010 Census. Tucson is the second-largest populated city in Arizona behind Phoenix, which both anchor the Arizona Sun Corridor. The city is located 108 miles (174 km) southeast of Phoenix and 60 mi (97 km) north of the U.S.-Mexico border. Tucson is the 33rd largest city and the 52nd largest metropolitan area in the United States. Roughly 150 Tucson companies are involved in the design and manufacture of optics and optoelectronics systems, earning Tucson the nickname Optics Valley.

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, 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.

The English name Tucson derives from the Spanish name of the city, Tucsón [tukˈson], which was borrowed from the O'odham name Cuk Ṣon [tʃʊk ʂɔːn], meaning "(at the) base of the black [hill]", a reference to an adjacent volcanic mountain. Tucson is sometimes referred to as "The Old Pueblo."