National Arizona Day Date in the current year: February 14, 2025

Arizona is one of the two states that form the core of the American Southwest; the other one is New Mexico. It is also one of the Mountain States, along with Colorado, Idaho, Montana, Nevada, New Mexico, Utah and Wyoming. Arizona was one of the last US territories to become a state. After its admission, Alaska and Hawaii were the only remaining US territories.

For thousands of years before the arrival of the first Europeans, the territory that is now Arizona was inhabited by numerous indigenous tribes. Notable Native American cultures that flourished in the region include the Hohokam, Mogollon, and the Ancestral Puebloan cultures.

Marcos de Niza, an Italian-born missionary and Franciscan friar, was the first European to set foot in Arizona and make contact with the natives in 1539. From 1540 to 1542, Francisco Vázquez de Coronado’s expedition explored the region. After that, Spanish settlers began migrating to Arizona. In the late 17th and early 18th centuries, Jesuit missionary Father Eusebio Kino established a series of missions and converted many of the locals to Christianity.

After Mexico gained independence from Spain in 1821, Arizona became part of the Mexican territory of Alta California (“Upper California”), also known as Nueva California (“New California”). The region remained under Mexican control until Mexico’s defeat in the Mexican-American War of 1846–1848.

According to the Treaty of Guadalupe Hidalgo, more than half of Mexican territory was ceded to the United States after the war. The ceded lands included most of what is now Arizona. In 1853, the United States acquired additional land from Mexico in the so-called Gadsden Purchase. This purchase included present-day southern Arizona.

Originally, the entirety of present-day Arizona was administered as part of the Territory of New Mexico. In 1858, members of the New Mexico territorial legislature voted in favor of creating the Arizona Territory, which would border New Mexico along the 109th meridian. Congress, however, wasn’t in a hurry to approve this decision.

The Arizona Territory split from New Mexico during the American Civil War. It joined the Confederate States and was formally organized on January 18, 1862. On February 24, 1863, the federal government officially approved the formation of the Arizona Territory. For most of the war, Arizona was under the control of troops from the California Column, while its Confederate government was in exile in San Antonio.

Arizona officially became the 48th state of the United States on February 14, 1912. It was the last of the contiguous states to be admitted to the Union. Although Arizona Statehood Day is not a public holiday and government offices remain open, the anniversary of Arizona’s admission to the union is celebrated with events and programs focusing on Arizona's history and culture.

An alternative celebration called National Arizona Day is held on June 21. It was created in 2017 by National Day Calendar as part of its National State Days project. Rather than celebrating states on their actual admission anniversaries, this project celebrates them in the order in which they joined the Union.