The history of life in the Tucson Valley begins ca. 10,000 B.C. with the migrations of Paleoindian and Archaic hunters and gatherers. Whether or not there was continuous habitation is unclear, though evidence of agricultural settlements along the Santa Cruz River have been found dating from ca. 1000 B.C.
Between A.D. 200 and 1450, the Hohokam culture thrives. The Pima and Tohono O'odham are the descendents of that advanced civilization, and have inhabited the region since the Hohokam decline. Around 1540 the Coronado Expedition crosses Arizona in search of the "Seven Cities of Gold."
Father Francisco Kino establishes the Mission San Xavier del Bac in 1699. It won't be until 1797 that it will be completed.
The Mission San Agustin, a "visita" of San Xavier, is established on the west bank of the Santa Cruz River in 1757. The construction of the mission and the convento is completed in 1790's.
1775, Hugo O'Conor establishes the Tucson Presido. This year marks the official birthdate of the City of Tucson. Tucson becomes part of Mexico when it fights for independence in 1821. After the Gadsden Purchase in 1854, Tucson falls under the jurisdiction of the United States.
Arizona becomes an official territory in 1863. Between 1867 and 1877, Tucson holds the title of territorial capitol.
In 1880, the Southern Pacific Railroad reaches Tucson. The population reaches 8,000.
Arizona becomes the 48th state in the Union in 1912.
By 1950 Tucson's population has reached 120,000 and by 1960 it nearly doubled to 220,000. The City and Pima County officially recognizes the city's history by adopting historic district ordinances in 1972.
Tucson becomes the 33rd largest U.S. city in 1990 as its population tops 400,000.
In 2016 the Tucson population has grown to 653,359.