In the year 1767, the township of Coleraine was one of the original five townships formed within Cumberland County's frontier region. It stretched from Evitts Mountain in the west to the eastern slope of the mountain range composed of Town Hill in the south and Rays Hill in the north. It stretched from Johns Branch of the Raystown Branch of the Juniata River and Harbor Mountain in the north to the provincial boundary line with Maryland in the south. Cumberland Township, also one of the original five townships, extended over Evitts Mountain at its south end. In 1783 Providence Township was formed out of the north end of Coleraine.
In the year 1799, Southampton Township was formed by the drawing of a surveyed line from the southeast at a point a short distance south of McKees Gap in Town Hill to the northwest where it intersected with Tussey Mountain a short distance north of Martin Hill that connects Evitts Mountain to Tussey. The western boundary line was run along the summit of Evitts Mountain, taking a sliver of Cumberland Township as a result.
Southampton Township's formation was described in the records of the Court of Quarter Sessions on 22 April 1799.
The Petition of a Number of the Inhabitance of the Townships of Cumberland Valley and Colerain in the County of Bedford aforesaid ~ Humbly Sheweth that Petitioners and Others in said Townships labour under many inconveniences by reason of the distance and Mountaineousness of said Townships ~ The Petitioners therefore pray that the Honourable Court would be pleased to Grant us a Township Beginning at the province line near the house of Joshua Lewman thence along the top of Evests Mountain to the Dividing Ridge between the waters of Flintstone and the Cove Creek about nine Miles thence along the top of said Ridge to [illegible] Mountain about too Miles thence along the top of said Mountain to the Dividing ridge between the waters of Town Creek & sideling hill Creek And the waters of Juniata about six miles thence along the top of Said ridge to the top of Town hill about ten Miles thence along the top of said hill to the province Line above ten miles and if the honourable Court will Grant and confirm the same according to the Laws of Pennsylvania made and Provided in such cases your Petitioner as in duty bound will ever pray &c. ~~~~~ And at April Sessions 1799 It is considered by the Court that a new township be divided and erected agreeably to the boundaries within stated and that the same be hereafter known and distinguished by the name & state of "Southampton:"
Southampton Township was reduced in size by about a third when Mann Township was formed in 1876 out of its eastern region.
The township was named for the city of Southampton in Hampshire, England.
