A brewer named Reuben Haines, a native of Philadelphia, founded the town of Northumberland in 1772, attempting to set it up as an English village.

The land that became Northumberland was purchased from the Iroquois in the first Treaty of Fort Stanwix in 1768, and the village was laid out in 1772.

During the American Revolution, Northumberland was evacuated during the Big Runaway in 1778, and only finally resettled in 1784.

[4] Northumberland was the American home of 18th-century British theologian, Dissenting clergyman, natural philosopher, educator, and political theorist Joseph Priestley (1733–1804) from 1794 until his death in 1804.

There is one other property in the borough on the NRHP: the Priestley-Forsyth Memorial Library, built by a great-grandson of Joseph Priestley.

A seven-seat Council governs the Borough of Northumberland, with a mayor taking on a largely ceremonial role.

The current mayor, Dan Berard, was elected to serve a second term in November 2023 and sworn in January 2024.