Miami is a major port city on the Atlantic coast of South Florida in the southeastern United States. As the seat of Miami-Dade County, the municipality is the principal, central, and the most populous city of the Miami metropolitan area and part of the second-most populous metropolis in the southeastern United States. According to the United States Census Bureau, Miami's metro area is the seventh-most populous and fourth-largest urban area in the U.S., with a population of around 5.5 million.