Mobile County is a county located in the southwestern corner of the U.S. state of Alabama. It is the third-most populous county in the state after Jefferson and Madison counties. As of the 2020 census, its population was 414,809. Its county seat is Mobile, which was founded as a deepwater port on the Mobile River. The only such port in Alabama, it has long been integral to the economy for providing access to inland waterways as well as the Gulf of Mexico.