Biography from Benson J. Lossing in his Pictorial Field-Book of the Revolution [with minor edits]:

William Polk, son of Colonel Thomas Polk of Mecklenburg, North Carolina, was born in that county in 1759. He was present at the celebrated Mecklenburg Convention in May of 1775. He joined the army early in 1777 and went to the north with General Nash, who was killed at Germantown. He was in the battles on the Brandywine and at Germantown, and was wounded at the latter place.

He went south with General Gates and was with him in the battle at Sander's Creek, near Camden. He was with Greene at Guilford and Eutaw. In the latter battle he received a wound, the effects of which he felt until his death.

At the close of the war, he returned to Charlotte, his native place, and in 1787 represented the county in the North Carolina Legislature. He subsequently removed to Raleigh, where he resided until his death. In 1812, President Madison offered him the commission of a brigadier, but, being opposed to the war, he declined the honor.

He died on January 14, 1835, in the seventy-sixth year of his age. Colonel Polk was the last surviving field officer of the North Carolina line. Bishop Leionidas Polk, of the Protestant Episcopal Church of Louisianan, and General Thomas G. Polk, of Mississippi, are his sons.