Sir John Juyn (died 24 March 1440), SL, was an English judge who served as Chief Justice of the King's Bench (1439–40).
[citation needed] Following the death of his father in 1390, Juyn inherited his estates in Bristol, Bedminster and Knowle.
His first appearance in surviving records was in 1407, as a mainpernor for a group of Bristolian merchants sued for debt by the City of London.
In 1436, he received an additional appointment as Justice of the Court of Common Pleas, from which time he switched to the Home Counties circuit.
In May 1426, he was knighted in Parliament, and acted as a trier of petitions there from 1425 to 1439, during which period he was summoned frequently to advise the King's Council, most notably for 15 days at the November 1426 Council at Reading, where he helped to draft laws to keep the peace between Humphrey, Duke of Gloucester and Henry Beaufort.