Maricopa County is located in the south-central part of the U.S. state of Arizona. As of the 2020 census, the county’s population was 4,420,568, making it the state's most populous county, and the fourth-most populous in the United States. It contains about 62% of Arizona's population, making Arizona one of the most centralized states in the nation. The county seat is Phoenix, the state capital and fifth-most populous city in the United States.