Brockton is a city in Plymouth County, Massachusetts, United States; the population was 105,643 at the 2020 United States census. Along with Plymouth, it is one of the two county seats of Plymouth 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. Campello is the smallest neighborhood, but also the most populous. Brockton hosts a baseball team, the Brockton Rox. It is the second-windiest city in the United States, with an average wind speed of 14.3 mph (23.0 km/h).

Plymouth County is a county in the U.S. state of Massachusetts, south of Boston. As of the 2020 census, the population was 530,819. Its county seats are Plymouth and Brockton. In 1685, the county was created by the Plymouth General Court, the legislature of Plymouth Colony, predating its annexation by the Massachusetts Bay Colony.