There are 31 US Post Offices in Pima County serving a total of 612,728 residents equating to 19,765 residents per post office. It's estimated that approximately 977,982 packages are handled across the 31 county post offices annually. Pima County /\u02c8pi\u02d0m\u0259/ is a county in the south central region of the U.S. state of Arizona. As of the 2010 census, the population was 980,263, making it the second-most populous county in Arizona. The county seat is Tucson, where nearly all of the population is centered. The county is named after the Pima Native Americans who are indigenous to this area. Pima County comprises the Tucson, AZ Metropolitan Statistical Area. Pima County contains parts of the Tohono O'odham Nation, as well as all of the San Xavier Indian Reservation, the Pascua Yaqui Indian Reservation, Organ Pipe Cactus National Monument, Ironwood Forest National Monument and Saguaro National Park. The vast majority of the county population lies in and around the city of Tucson (2011 city population: 525,796), 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 41,335), Marana (population 35,232), Sahuarita (population 25,458), and South Tucson (population 5,695), 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.