Plymouth County was established in 1685 when Plymouth Colony was divided into three counties: Plymouth, Bristol, and
Barnstable. Plymouth County included the towns of Plymouth (inc. 1620), Scituate (inc. 1636), Duxbury (inc. 1637),
Marshfield (inc. 1640), Bridgewater (inc. 1656), and Middleborough (inc. 1669).
The county remained unchanged for over twenty years when the town of Plympton was set off from Plymouth, incorporated
1707, and the town of Rochester (inc. 1686), by petition to the court, was transferred to Plymouth County from Barnstable
County. The next changes took place a few years later when the town of Pembroke was set off from Duxbury, and the town of
Abington was set of from Bridgewater, both incorporated in 1712.
It remained the same for over a decade when Kingston was set off from Plymouth, incorporated in 1726, and Hanover was set off
from Scituate, incorporated in 1727.
Almost another decade went by before the next changes incurred. Halifax, set off from parts of Plympton, Middleborough,
and Pembroke, was incorporated in 1734. Then in 1739, the town of Wareham, made up of part of Rochester and part of the
Agawam Purchase, was officially incorporated.
Two more changes took place before the end of the 1700's. First, the town of Carver was set off from Plympton and
incorporated in 1790, and second, part of Stoughton, which was located in Norfolk County, was set off to the town of
Bridgewater in 1798, creating the final boundaries of Plymouth County entering the next century.
In 1793, a new county was formed by the name of Norfolk which was to include all the towns that were part of Suffolk County,
except for Boston and Chelsea. Cohasset had already been set off from Hingham by this time and was on the list of towns to
become part of Norfolk County along with Hingham and Hull, another town that had been previously set off from Hingham.
Apparently the residents of Hingham (inc. 1635) and Hull (inc. 1644) were disgruntled over this decision and wished to be
transferred to Plymouth County. They finally got their wish in 1803 when Hingham and Hull officially became a part of Plymouth
Continuing into the 1800's saw numerous new towns being set off from those well established: Hanson set off from Pembroke,
incorporated 1820; North Bridgewater set off from Bridgewater, incorporated 1821; West Bridgewater set off from Bridgewater,
incorporated 1822; East Bridgewater set off from Bridgewater, incorporated 1823; South Scituate set off from Scituate,
incorporated 1849; Marion set off from Rochester, incorporated 1852; Lakeville set off from Middleborough, incorporated
1853; Mattapoisett set of from Rochester, incorporated 1857; Rockland set off from Abington, incorporated 1874; South
Abington set off from Abington and East Bridgewater, incorporated 1875.
The final changes that basically make up the Plymouth County of today occurred in the latter half of the 1800's and are all
name changes: North Bridgewater changed their name to Brockton in 1874 (inc. as city in 1881); South Abington changed their
name to Whitman in 1886; and South Scituate changed their name to Norwell 1888.
The City of Brockton and the Town of Plymouth are the two county seats in Plymouth County.
(Data from official state and town websites)