William Henn (c. 1720 – 1796) was an Irish judge, who is remembered now mainly for the somewhat malicious description of him in Sir Jonah Barrington's Personal Sketches.

[2] They had a long association with the law: Henry Hene, or Henn, who is generally thought to have been William's direct ancestor, was Chief Baron of the Irish Exchequer 1680–1687.

[3] William entered Middle Temple in 1738, took his degree as Bachelor of Arts from Trinity College Dublin in 1740, was called to the Irish Bar in 1744 and became King's Counsel in 1762.

According to Barrington, Henn was "dreadfully puzzled" when he was hearing a case while on assize at Wexford in about 1789 by the arguments of two young barristers, each of whom pleaded with great eloquence that the law was in his client's favour.

[4] John Scott, 1st Earl of Clonmell, who presided in the King's Bench where Henn was a junior judge, had a very low opinion of him, calling him "at best a fool".