Arizona is a landlocked state in the Southwestern United States, sharing the Four Corners region with Colorado, New Mexico, and Utah. It also borders Nevada to the northwest and California to the west, and shares an international border with the Mexican states of Sonora and Baja California to the south and southwest. Its capital and largest city is Phoenix, which is the most populous state capital and fifth-most populous city in the United States. Arizona is divided into 15 counties.
Arizona is the sixth-largest state by area and the 14th-most-populous of the 50 states. It is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of Alta California and Nuevo México in New Spain (Spanish Empire), it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848, where the area became part of the New Mexico Territory. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.
Southern Arizona is known for its desert climate, with extremely hot summers and mild winters. Northern Arizona features forests of pine, Douglas fir, and spruce trees; the Colorado Plateau; mountain ranges (such as the San Francisco Mountains); as well as large, deep canyons, with much more moderate summer temperatures and significant winter snowfalls. There are ski resorts in the areas of Flagstaff, Sunrise, and Tucson. In addition to the internationally known Grand Canyon National Park, which is one of the world's seven natural wonders, there are several national forests, national parks, and national monuments.
Arizona is home to a diverse population. About one-quarter of the state is made up of Indian reservations that serve as the home of 27 federally recognized Native American tribes, including the Navajo Nation, the largest in the state and the country, with more than 300,000 citizens. Since the 1980s, the proportion of Hispanics has grown significantly owing to migration from Mexico and Central America. A substantial portion of the population are followers of the Roman Catholic Church and the Church of Jesus Christ of Latter-day Saints. Arizona's population and economy have grown dramatically since the 1950s because of inward migration, and the state is now a major hub of the Sun Belt. Many large companies, such as PetSmart and Circle K, have headquarters in the state, and Arizona is home to major universities, including the University of Arizona, Arizona State University, and Northern Arizona University.
The state's name appears to originate from an earlier Spanish name, Arizonac, derived from the O'odham name alĭ ṣonak, meaning 'small spring'. Initially this term was applied by Spanish colonists only to an area near the silver mining camp of Planchas de Plata, Sonora. To the European settlers, the O'odham pronunciation sounded like Arissona. The area is still known as alĭ ṣonak in the O'odham language.
Another possible origin is the Basque phrase haritz ona 'the good oak', as there were numerous Basque shepherds in the area. A native-born Mexican of Basque ancestry established the ranchería (small rural settlement) of Arizona between 1734 and 1736 in the current Mexican state of Sonora. It became notable after a significant discovery of silver there around 1737.
For thousands of years before the modern era, Arizona was home to many ancient Native American civilizations. Hohokam, Mogollon, and Ancestral Puebloan cultures were among those that flourished throughout the state. Many of their pueblos, cliffside dwellings, rock paintings and other prehistoric treasures have survived and attract thousands of tourists each year.
In 1539, Marcos de Niza, a Spanish Franciscan, became the first European to contact Native Americans. He explored parts of the present state and made contact with native inhabitants, probably the Sobaipuri. The expedition of Spanish explorer Coronado entered the area in 1540–1542 during its search for Cíbola. One of the first settlers in Arizona was José Romo de Vivar.
Father Kino was the next European in the region under Spanish rule. A member of the Society of Jesus ("Jesuits"), he led the development of a chain of missions in the region. He converted many of the Indians to Christianity in the Pimería Alta (now southern Arizona and northern Sonora) in the 1690s and early 18th century. Spain founded presidios ("fortified towns") at Tubac in 1752 and Tucson in 1775.
When Mexico achieved its independence from the Kingdom of Spain and its Spanish Empire in 1821, what is now Arizona became part of its Territory of Nueva California, ("New California"), also known as Alta California ("Upper California"). Descendants of ethnic Spanish and mestizo settlers from the colonial years still lived in the area at the time of the arrival of later European-American migrants from the United States.
During the Mexican–American War (1847–1848), the U.S. Army occupied the national capital of Mexico City and pursued its claim to much of northern Mexico, including what later became Arizona Territory in 1863 and later the State of Arizona in 1912. The Treaty of Guadalupe Hidalgo (1848) specified that, in addition to language and cultural rights of the existing inhabitants of former Mexican citizens being considered as inviolable, the sum of $15 million in compensation (equivalent to $558,173,076.92 in 2025) be paid to the Republic of Mexico. In 1853, the U.S. acquired the land south below the Gila River from Mexico in the Gadsden Purchase along the southern border area as encompassing the best future southern route for a transcontinental railway.
What is now the state of Arizona was administered by the United States government as part of the Territory of New Mexico from 1850 until the southern part of that region seceded from the Union to form the Territory of Arizona. This newly established territory was formally organized by the federal government of the Confederate States on Saturday, January 18, 1862, when President Jefferson Davis approved and signed An Act to Organize the Territory of Arizona, marking the first official use of the name "Territory of Arizona". The Southern territory supplied the Confederate government with men, horses, and equipment. Formed in 1862, Arizona scout companies served with the Confederate States Army during the American Civil War. Arizona has the westernmost military engagement on record during the Civil War with the Battle of Picacho Pass (1862).
The Federal government declared a new U.S. Arizona Territory, consisting of the western half of earlier New Mexico Territory, in Washington, D.C., on February 24, 1863. These new boundaries would later form the basis of the state. The first territorial capital, Prescott, was founded in 1864 following a gold rush to central Arizona. The capital was later moved to Tucson, back to Prescott, and then to its final location in Phoenix in a series of controversial moves as different regions of the territory gained and lost political influence with the growth and development of the territory.
Although names including "Gadsonia", "Pimeria", "Montezuma" and "Arizuma" had been considered for the territory, when 16th President Abraham Lincoln signed the final bill, it read "Arizona", and that name was adopted. (Montezuma was not derived from the Aztec emperor, but was the sacred name of a divine hero to the Akimel O'odham of the Gila River Valley. It was probably considered – and rejected – for its sentimental value before Congress settled on the name "Arizona".)
Brigham Young, leader of the Church of Jesus Christ of Latter-day Saints in Salt Lake City, Utah, sent Mormons to Arizona in the mid- to late 19th century. They founded Mesa, Snowflake, Heber, Safford, and other towns. They also settled in the Phoenix Valley (or "Valley of the Sun"), Tempe, Prescott, and other areas. The Mormons settled what became northern Arizona and northern New Mexico. At the time these areas were in a part of the former New Mexico Territory.