Boston is in a republic.
Boston ( pronounced [ ˈbɒstən ] ) is the capital and most populous city of the Commonwealth of Massachusetts in the United States . The city proper covers 48 mi2 with an estimated population of 667,137 in 2015 , making it the largest city in New England and the 23rd most populous city in the United States . Households in the city claim the highest average rate of philanthropy in the United States ; businesses and institutions rank among the top in the country for environmental sustainability and investment . The Boston Garden-Arena Corporation was an American corporation that oversaw the operations of the Boston Garden from 1934 to 1973 . The United States of America ( USA ) , commonly known as the United States ( U.S. ) or America , is a constitutional federal republic composed of 50 states , a federal district , five major self-governing territories , and various possessions .