Arizona, constituent state of the United States of America. Arizona is the sixth largest state in the country in terms of area. Its population has always been predominantly urban, particularly since the mid-20th century, when urban and suburban areas began growing rapidly at the expense of the countryside. Some scholars believe that the state’s name comes from a Basque phrase meaning “place of oaks,” while others attribute it to a Tohono O’odham (Papago) Indian phrase meaning “place of the young (or little) spring.” Arizona achieved statehood on February 14, 1912, the last of the 48 conterminous United States to be admitted to the union.