Brockton, Massachusetts Library system. The main library is a Carnegie building and is located at 304 Main Street, and there are two branch libraries. Brockton, Massachusetts Brockton is a city in Plymouth County, Massachusetts, United States; the population was 95,314 in the 2015 Census. Brockton, along with Plymouth, are the county seats of Plymouth County. Brockton is the seventh 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 of the villages within the city
Brockton, Massachusetts and 14.5% of the population were below the poverty line, including 19.4% of those under age 18 and 12.6% of those age 65 or over. Statistically, Brockton is the most populous and most densely populated community in Plymouth County. It is the sixth largest community in the commonwealth, the largest of the sub-100,000 person cities. However, it is only the twenty-seventh most densely populated community in the Commonwealth. Data is from the 2009-2013 American Community Survey 5-Year Estimates. On the national level, Brockton is a part of Massachusetts's 8th congressional district, and has been represented since 2001 by Stephen Lynch.