U.S. Congress made Arizona a U.S. territory in 1863 and the first capital was Fort Whipple. In May 1864, the territory was moved to Prescott. In 1867, the territorial capital was moved to Tucson. In 1877, the capital was moved back to Prescott. Finally, Phoenix was declared the permanent capital starting February 4, 1889. Phoenix is also Arizona's most populous city.