Plymouth County, Massachusetts (Plymouth Colony)

Plymouth County is located along the western shores of Cape Cod Bay. Originally a part of Plymouth Colony, it was formed on 2 June 1685, along with the counties of Barnstable and Bristol, by the legislature of Plymouth Colony in preparation for its 7 October 1691 annexation by the Massachusetts Bay Province. At its creation, Plymouth County was composed of the towns of Plymouth, Bridgewater, Duxbury, Marshfield, Middleborough (incorporated in 1669 as Middleberry), and Scituate.

Over time, communities were subdivided forming new towns and villages, county boundaries were redefined and changes also occurred as land was acquired from and lost to other counties. Some of Plymouth County's additions included: the town of Rochester from Barnstable County On 19 November 1707; a small non-county area lying between Bristol and Plymouth counties on 29 October 1708; two pieces of land annexed by Bridgewater from Stoughton on 20 November 1770 and 8 February 1798, moving that land from Suffolk to Plymouth County; the towns of Hingham and Hull from Norfolk County on 18 June 1803 (both in Suffolk County before joining Norfolk County in 1793); land Scituate annexed from Cohasset on 20 March 1840, moving that area from Norfolk to Plymouth County, while previously, land annexed by Cohasset from Scituate on 14 June 1823, had moved that area from Plymouth to Norfolk County.

County boundaries of special interest to us in our research include the "Old Colony Line" and the changing boundaries between Plymouth and its neighboring Norfolk, Bristol and Barnstable counties. On 18 March 1711/12, the "Old Colony Line" that had previously divided Massachusetts Bay and Plymouth colonies was declared, with no changes, as the official border between Suffolk, Bristol, and Plymouth counties.

The boundaries between Plymouth and Norfolk counties changed on 31 March 1847 when Abington and Weymouth redefined their border, and on 30 April 1897 and 23 March 1928, when the border between Hingham and Cohasset was twice redefined.

The boundaries between Plymouth and Bristol counties changed on 1 June 1867 when Taunton and Lakeville redefined their border, and on 9 April 1836, when Rochester and Fairhaven redefined theirs. Barnstable and Plymouth county borders changed on 14 April 1897 when the boundary between Wareham and Bourne was redefined.