Miami is a major city in southeastern Florida, in the United States. The city covers 55.27 square miles (143.15 km²) and is the county seat of Miami-Dade County. Miami is a gamma world city with an estimated population of 404,048. It is the largest city within the South Florida metropolitan area, which is the largest metropolitan area in the Southeastern United States with 5.4 million. Miami and its surrounding cities make up the fifth largest urban area in the United States.