Dorchester (/ˈdɔːrtʃɛstər/) is a neighborhood comprising more than 6 square miles (16 km) in the city of Boston, Massachusetts, United States. Originally, Dorchester was a separate town, founded by Puritans who emigrated in 1630 from Dorchester, Dorset, England, to the Massachusetts Bay Colony. This dissolved municipality, Boston's largest neighborhood by far, is often divided by city planners in order to create two planning areas roughly equivalent in size and population to other Boston neighborhoods.
Founded in 1630, just a few months before the founding of the city of Boston, Dorchester now covers a geographic area approximately equivalent to nearby Cambridge. When annexed to Boston in 1870, Dorchester was still a primarily rural town and had a population of 12,000. Construction of railroad and commuter streetcar lines brought rapid growth, increasing the population to 150,000 by 1920. In the 2010 United States census, the neighborhood's population was 92,115.