Brockton is a city in Plymouth County, Massachusetts, United States. Its population was 105,643 at the 2020 United States census, and it is a major economic and commercial hub for the southern part of Greater Boston. Along with Plymouth, it is one of the two county seats of the county. It is the sixth-largest city in Massachusetts and is sometimes referred to as the "City of Champions", due to the success of native boxers Rocky Marciano and Marvin Hagler, as well as its successful Brockton High School sports programs. Two villages within it are Montello and Campello, both of which have MBTA Commuter Rail Stations and post offices.