Boston, officially the City of Boston, is the capital and most populous city in the Commonwealth of Massachusetts, and is the cultural & financial …Boston, officially the City of Boston, is the capital and most populous city in the Commonwealth of Massachusetts, and is the cultural & financial center of New England in the Northeastern United States, with an area of 48.4 sq mi and a population of 675,647 in 2020. The Greater Boston metropolitan statistical area is the eleventh-largest in the country.