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 and is an independent city that is not part of any county. With a population of 617,734 in 2017, Baltimore is the largest independent city in the United States. As of 2016, the population of the Baltimore metropolitan area was estimated to be just under 2.8 million, making it the 21st largest metropolitan area in the country. Baltimore is located about 40 miles northeast of Washington, D.C., making it a principal city in the Washington-Baltimore combined statistical area, the fourth largest CSA in the nation with a calculated 2016 population of 9,665,892.Founded in 1729, Baltimore is the second-largest seaport in the Mid-Atlantic. The city's Inner Harbor was once the second leading port of entry for immigrants to the United States and a major manufacturing center.