

The British purchased land from the Iroquois in the Treaty of Fort Stanwix of 1768, opening what is now Lycoming County to settlement.

The lands of the West Branch Susquehanna River valley were then chiefly occupied by the Munsee clan or phratry of the Lenape, and were under the nominal control of the Five (later Six) Nations of the Iroquois. Decimated by diseases and warfare, they had died out, moved away, or been assimilated into other tribes by the early 18th century. Their name meant "people of the muddy river" in Algonquian. The first recorded inhabitants of the Susquehanna River valley were the Iroquoian speaking Susquehannocks. The land had previously been part of Armstrong Township.

On November 29, 1886, the Lycoming County court incorporated the villages of Rocktown, Billman, and vicinities as the borough of South Williamsport. South Williamsport celebrated the centennial of its incorporation as a borough in 1986.
