Miami-Dade County is a county in the southeastern part of the U.S. state of Florida. It is the southeasternmost county on the U.S. mainland. According to a 2017 census report, the county had a population of 2,751,796, making it the most populous county in Florida and the seventh-most populous county in the United States. It is also Florida’s third largest county in terms of land area, with 1,946 square miles (5,040 km2). The county seat is Miami, the principal city in South Florida.