The State of Westmoreland was a proposed self-proclaimed state that would have seceded from Pennsylvania.
Both Pennsylvania and Connecticut claimed ownership of the lands between 41° N and 42° N, and this gave rise to a series of land-conflicts collectively referred to as the Yankee-Pennamite Wars. By the conclusion of the American Revolutionary War, the states had made conflicting land grants in the region and independently organized it politically, with Connecticut creating a County of Westmoreland, seated in the Connecticut-settled Wyoming Valley, while Pennsylvania included the settled regions in its Northumberland County. The Congress of the Confederation was asked to decide on the legal owner. With the Decree of Trenton on December 30, 1782, the confederation government officially decided that the region belonged to Pennsylvania. Pennsylvania then ruled that the Connecticut settlers ("Yankees") were not citizens of the Commonwealth, could not vote, and were to give up their property claims.
In May 1784, the Connecticut settlers were force-marched away from the valley. In November, they returned with a greater force and captured and destroyed Fort Dickinson. With that victory, Captain John Franklin proposed that a new state separate from Connecticut and Pennsylvania be created, to be called Westmoreland.
To avoid further armed conflict the Commonwealth of Pennsylvania reversed its earlier decision and agreed that Yankee property claims that predated the Decree of Trenton should be honored, with compensation in the form of fresh grants being awarded those holding conflicting Pennsylvania claims. Most Connecticut Yankees accepted the proposed compromise, part of which involved separating a sizable part of Northumberland County to create a new county. On September 23, 1786, the Pennsylvania General Assembly created Luzerne County, named for the French minister the Chevalier de la Luzerne. This newly created county encompassed a large area; Lackawanna, Wyoming, Susquehanna, and part of Bradford County would all eventually be separated out as independent counties. While this compromise brought an end to the proposed state, political discord associated with the conflict continued into the 19th century.
Note that both Westmoreland County, Connecticut and the proposed State of Westmoreland are unrelated to the current Westmoreland County located in southwestern Pennsylvania, which was created by an Act of the Assembly and approved by Governor of Pennsylvania Richard Penn on February 26, 1773.