Arizona is a state of the United States of America located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix. The second largest city is Tucson, followed in size by the eight Phoenix metropolitan area cities of Mesa, Glendale, Chandler, Scottsdale, Gilbert, Tempe, Peoria, Surprise and then by Yuma in Yuma County. Arizona is one of the Four Corners states.