Tucson is a city and the seat of Pima County, Arizona, United States, located 118 miles (188 km) southeast of Phoenix. As of July 1, 2005 a census estimate put the city's population at 521,605, and the metropolitan population at 931,210. By 2008 the city population is expected to exceed 610,000, while the metropolitan population is expected to exceed 1 million by spring 2007. In 2005 Tucson ranked as the 32nd-largest city and 52nd-largest metropolitan area in the U.S. It is the largest city in southern Arizona, and the second largest in the state after Phoenix.

Major incorporated suburbs of Tucson include Oro Valley and Marana northwest of the city, South Tucson (surrounded by Tucson), and Sahuarita south of the city. Communities in the vicinity of Tucson (some within or overlapping the city limits, and some incorporated in their own right) include Casas Adobes, Catalina, Catalina Foothills, Flowing Wells, Green Valley, Tanque Verde, and Vail.

The name Tucson originates via Spanish from the O'odham, roughly, "chuk shon"), meaning "Black Base," a reference to the mostly volcanic mountains on the west side of the city. The most notable of these mountains is Sentinel Peak, better known as "A Mountain" because it sports a large letter A in honor of the nearby University of Arizona, situated in west central Tucson. Tucson is sometimes referred to as "The Old Pueblo."

According to the United States Census Bureau, the city has a total area of 195.1 mi. 194.7 mi. of it is land and .4 mi of it (0.22%) is water.

Its elevation is 2,389 ft (728 m) above sea level. Tucson is situated on an alluvial plain, surrounded by five minor ranges of mountains: the Santa Catalina Mountains and the Tortolita Mountains to the north, the Santa Rita Mountains to the south, the Rincon Mountains to the east, and the Tucson Mountains to the west. The Santa Catalina Mountains include Mount Lemmon, the southernmost ski destination in the continental U.S.

The city is located on the Santa Cruz River, a dry river bed much of the year that floods during significant seasonal rains. (The Santa Cruz becomes a subterranean stream part of the year although it may appear dry.)

Tucson is located along I-10, which runs through Phoenix toward Santa Monica, California in the northwest, and through El Paso, Texas toward Jacksonville, Florida in the east. I-19, runs south from Tucson toward Nogales and the U.S.-Mexico border.