Sir William Fairfax (1609 – 19 September 1644), was an officer in the Parliamentary army during the English Civil War.

[2] He was given the command of a regiment in the army of Essex, which was stationed on the left wing at the Battle of Edgehill and ran away.

[4] In the victory at Nantwich (25 January 1644) Sir William Fairfax commanded a wing of the horse, and at Marston Moor headed a brigade of foot on the right of the parliamentary line.

[5] In August 1644 he was despatched into Lancashire with two thousand Yorkshire horse, and took part in the siege of Liverpool.

In the Relief of Montgomery Castle on 18 September 1644, he was mortally wounded, and died the following day.