Pima County is located in the south central part of the U.S. state of Arizona. The county is named after the Pima American Indian tribe which was indigenous to the area. As of the 2005 U.S. Census estimate, the population was 957,635. The county seat is Tucson, where nearly all of the population is centered.

Pima County contains parts of the Tohono O'odham Nation, as well as all of the San Xavier Indian Reservation and Organ Pipe Cactus National Monument and Saguaro National Park.

The vast majority of the county population lies in and around the city of Tucson (2005 city population: 529,770), filling much of the eastern part of the county with urban development. Tucson, Arizona's second largest city, is a major commercial and academic center. Other urban areas include the Tucson suburbs of Oro Valley (population 39,400), Marana (population 26,725), Sahuarita (population 13,990), and South Tucson (population 5,630), a large ring of unincorporated urban development, and the growing satellite town Green Valley. The rest of the county is sparsely populated; the largest towns are Sells, the capital of the Tohono O'odham Nation, and Ajo in the far western region of the county.

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 the Arizona Territory of the United States. The original county included all of southern Arizona from the western Colorado River to the Gila River in the north to the Mexican international border in the south and east to the New Mexico state line. Soon thereafter, the counties of Cochise, Graham and Santa Cruz were carved from the original Pima County.

As of the census? of 2000, there were 843,746 people, 332,350 households, and 212,039 families residing in the county. The population density was 35/km? (92/mi?). There were 366,737 housing units at an average density of 15/km? (40/mi?). The racial makeup of the county was 75.07% White, 3.03% Black or African American, 3.22% Native American, 2.04% Asian, 0.13% Pacific Islander, 13.30% from other races, and 3.21% from two or more races. 29.34% of the population were Hispanic or Latino of any race.

There were 332,350 households out of which 29.20% had children under the age of 18 living with them, 47.70% were married couples living together, 11.80% had a female householder with no husband present, and 36.20% were non-families. 28.50% of all households were made up of individuals and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 3.06.

In the county the population was spread out with 24.60% under the age of 18, 10.90% from 18 to 24, 28.40% from 25 to 44, 21.90% from 45 to 64, and 14.20% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.70 males. For every 100 females age 18 and over, there were 92.70 males.

The median income for a household in the county was $36,758, and the median income for a family was $44,446. Males had a median income of $32,156 versus $24,959 for females. The per capita income for the county was $19,785. About 10.50% of families and 14.70% of the population were below the poverty line, including 19.40% of those under age 18 and 8.20% of those age 65 or over.