Arizona is a state of the United States, located in the southwestern region of the country. Arizona is also part of the Western United States and of the Mountain West states. Arizona is the sixth most extensive and the 16th most populous of the 50 states. Its capital and largest city is Phoenix. The second largest city is Tucson, followed in population by eight cities of the Phoenix metropolitan area: Mesa, Chandler, Glendale, Scottsdale, Gilbert, Tempe, Peoria, and Surprise.