Boston is in the United States.
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 . The city has one of the highest costs of living in the United States as it has undergone gentrification , though it remains high on world livability rankings .