Pima County, one of the four original counties in Arizona, was created in 1864 when land acquired by the Gadsden Purchase from Mexico in 1853 became Arizona Territory of the United States.  The original Pima county included approximately all of southern Arizona from the western Colorado River to the Gila River in the north to the Mexican border in the south and east to the New Mexico border.  Subsequently the counties of Cochise, Graham and Santa Cruz were carved from the original Pima County.  The Arizona Territory became a state in 1912. There are relatively few public records prior to statehood. 

European settlement of the region goes back to the arrival in the 1690s of Spaniards who encountered Native Americans already living here. The native people called themselves the Tohono O’odham (the desert people). Names given to these people by the Spaniards were Papago and Pima Indians.   The O'odham lived along the Santa Cruz and Gila Rivers and were mostly farmers.  They were frequently terrorized and raided by their more war-like neighbors to the east and southeast, the Apache.

About the middle of the 18th century, silver and gold were discovered in the  region and prospectors from Mexico entered the area in droves. The latter part of the century saw expansion of mining and ranching in Pima County and an  increase in population, despite the threat of attack from roaming bands of Apaches. The Royal Presidio de San Augustin del Tucson was completed by 1781, and it remained the northern most military outpost of Mexico until the arrival of American soldiers in 1856.

Several groups are attempting to make the pre-territorial history more accessible on the internet.

Some good sites for researching the early colonial period are the Rio Nuevo Project the Spanish Mission Project of the Interior Department  and the Arizona State Museum’s Documentary  Relations of the Southwest Project.

From a population of 395 in 1820, Tucson has grown to be the second largest city in Arizona.  It is by far the largest city in Pima County.   It has always served as the Pima County seat and was the Arizona Territorial capital from 1867 to 1877. Tucson is home to Davis Monthan Air Force Base the University of Arizona and many historical and cultural attractions which draw people to the area.Tucson City Website