Maricopa County ( ) is a county in the south-central part of the U.S. state of Arizona. As of the 2010 census, its population was 3,817,117, making it the state's most populous county, and the fourth-most populous in the United States. It is more populous than 23 states. The county seat is Phoenix, the state capital and fifth-most populous city in the country.
Maricopa County is in arizona