In April 1860, impatient for Congress to act, a convention of 31 delegates met in Tucson and adopted a constitution for a provisional territorial government of the area south of 34°N.

The Confederacy regarded the territory as a valuable route for possible access to the Pacific Ocean, with the specific intention of capturing California.

In July 1861, a small Confederate force of Texans under the command of Lieutenant Colonel John R. Baylor assaulted Fort Fillmore at Mesilla in the eastern part of the territory.

The legislation passed on January 13, 1862, and the territory was officially created by proclamation of President Jefferson Davis on February 14.

The following month, in March 1862, the U.S. House of Representatives, now devoid of the southern delegates and controlled by Republicans, passed a bill to create the United States Arizona Territory using the north–south border of the 109th meridian.

In 1867, though, Congress transferred the Arizona Territory's northwestern corner, specifically most of its land west of the Colorado River, to the state of Nevada.

A preliminary census will forthwith be taken, and thereafter the Judicial Districts will be formed, and an election of members of the Legislative Assembly, and the other officers provided by the Act be ordered.

I invoke the aid and cooperation of all Citizens of the Territory in my efforts to establish a government whereby the security of life and property will be maintained throughout its limits, and its varied resources be rapidly and successfully developed.