United States contains Miami.
Miami . 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 a 2009 UBS study of 73 world cities , Miami was ranked as the richest city in the United States , and the world 's fifth-richest city in terms of purchasing power . United States . The capital is Washington , D.C. , and the largest city is New York City ; nine other major metropolitan areas -- each with at least 4.5 million inhabitants and the largest having more than 13 million people -- are Los Angeles , Chicago , Dallas , Houston , Philadelphia , Miami , Atlanta , Boston , and San Francisco .