Plymouth (historically known as Plimouth and Plimoth) is a town in Plymouth County, Massachusetts, United States. It is the largest municipality in Massachusetts by area. The population was 51,701 at the 2000 census, with its estimated 2007 population being 57,901. Plymouth is one of two county seats of Plymouth County, the other being Brockton. It is named after Plymouth, Devon, United Kingdom, which is, in turn, named for the mouth of the river Plym. Plymouth was first settled by the Pilgrims in 1620. The first Thanksgiving was held there. It was the capitol of Plymouth Colony from 1620 until 1691, when it became part of Massachusetts. Plymouth was an important port in the 18th and 19th centuries.