Boston is the capital of the U.S. state of Massachusetts, officially the Commonwealth of Massachusetts, and is the state’s largest city, and the county seat of Suffolk County in the United States. The largest city in New England, the city proper, covering 48 square miles (125 square km), had an estimated population of 626,000 in 2011 according to the U.S. Census, making it the 21st largest city in the United States.