Maricopa County (/ˌmærɪˈkoʊpə/ MARR-i-KOH-pə) 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. It is more populous than 23 states.
The county seat is Phoenix, the state capital and fifth-most populous city in the country.