Tucson ( /ˈtuːsɒn/ TOO-son) is the county seat of Pima County, Arizona, United States, and is the home to University of Arizona. The 2010 United States Census puts the city's population at 520,116, while the 2011 estimated population of the entire Tucson metropolitan area was 989,569. Tucson is the second-largest populated city in Arizona behind Phoenix, which both anchor the Arizona Sun Corridor. The city is located 118 miles (188 km) southeast of Phoenix and 60 miles (98 km) north of the U.S.-Mexico border. Tucson is the 32nd largest city and 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.