Baltimore is the largest city in the U.S. state of Maryland, and the 30th-most populous city in the United States. Baltimore was established by the Constitution of Maryland[9] and is an independent city that is not part of any county. With a population of 611,648 in 2017, Baltimore is the largest independent city in the United States. As of 2017, the population of the Baltimore metropolitan area was estimated to be just under 2.808 million, making it the 20th largest metropolitan area in the country.[10] Baltimore is located about 40 miles (60 km) northeast of Washington, D.C., making it a principal city in the Washington-Baltimore combined statistical area (CSA), the fourth-largest CSA in the nation, with a calculated 2017 population of 9,764,315.[11]