Arizona is a state in the southwestern region of the United States. It is also part of the Western United States and of the Mountain West states. It is the sixth most extensive and the 15th 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.