Tucson is the county seat of and the most populated city in Pima County, Arizona, United States. It is the second-most populous city in Arizona with a population of 542,630 at the 2020 census, behind the capital city, Phoenix, while the Tucson metropolitan statistical area has an estimated 1.08 million residents and is the 52nd-largest metropolitan area in the United States. Tucson and Phoenix anc…