Pinal County is a county in the central part of the U.S. state of Arizona. According to the 2020 census, the population of the county was 425,264, making it Arizona's third-most populous county. The county seat is Florence. The county was established in 1875. Pinal County contains parts of the Tohono Oʼodham Nation, the Gila River Indian Community and the San Carlos Apache Indian Reservation, as well as all of the Ak-Chin Indian Community.