William Willoughby, 5th Baron Willoughby de Eresby

William Willoughby, 5th Baron Willoughby de Eresby
Arms of Sir William de Willoughby, 5th Baron Willoughby d'Eresby, KG.
Spouse(s)	Hon. Lucy Lestrange Lady Joan Holland
Issue Robert Willoughby, 6th Baron Willoughby de Eresby Sir Thomas Willoughby Elizabeth Willoughby, Baroness Beaumont Margery Willoughby, Baroness FitzHugh Margaret Willoughby, Lady Skipwith
Noble family	Willoughby de Eresby
Father	Robert Willoughby, 4th Baron Willoughby de Eresby
Mother	Margery la Zouche
Born	c.1370
Died	4 December 1409 Newcastle upon Tyne

William Willoughby, 5th Baron Willoughby de Eresby KG (c. 1370 – 4 December 1409) was an English baron.

William Willoughby was the son of Robert Willoughby, 4th Baron Willoughby de Eresby, by his first wife, Margery la Zouche, the daughter of William la Zouche, 2nd Baron Zouche of Harringworth, by Elizabeth de Roos, daughter of William de Roos, 2nd Baron de Roos of Hemsley, and Margery de Badlesmere (1306–1363), eldest sister and co-heir of Giles de Badlesmere, 2nd Baron Badlesmere. He had four brothers: Robert, Sir Thomas (died c. 20 August 1417), John and Brian.

After the death of Margery la Zouche, his father the 4th Baron married, before 9 October 1381, Elizabeth le Latimer (d. 5 November 1395), suo jure 5th Baroness Latimer, daughter of William Latimer, 4th Baron Latimer, and widow of John Neville, 3rd Baron Neville de Raby, by whom the 4th Baron had a daughter, Margaret Willoughby, who died unmarried. By her first marriage Elizabeth Latimer had a son, John Neville, 6th Baron Latimer (c.1382 – 10 December 1430), and a daughter, Elizabeth Neville, who married her step-brother, Sir Thomas Willoughby (died c. 20 August 1417).

The 4th Baron died on 9 August 1396, and Willoughby inherited the title as 5th Baron, and was given seisin of his lands on 27 September.

Hicks notes that the Willoughby family had a tradition of military service, but that the 5th Baron 'lived during an intermission in foreign war and served principally against the Welsh and northern rebels of Henry IV'. Willoughby joined Bolingbroke, the future King Henry IV, soon after his landing at Ravenspur, was present at the abdication of Richard II in the Tower on 29 September 1399, and was one of the peers who consented to King Richard's imprisonment. In the following year he is said to have taken part in Henry IV's expedition to Scotland.