Edward Plunkett (Dunsany), known to his family as "Eddie," was the first son of John William Plunkett, 17th Baron of Dunsany (1853–1899), and his wife, Ernle Elizabeth Louisa Maria Grosvenor Ernle-Erle-Drax, née Ernle Elizabeth Louisa Maria Grosvenor Burton (1855–1916).From a historically wealthy and famous family, Lord Dunsany was related to many well-known Irish figures. He was a kinsman of the Catholic Saint Oliver Plunkett, the martyred Archbishop of Armagh whose ring and crozier head are still held by the Dunsany family. He was also related to the prominent Anglo-Irish unionist and later nationalist / Home Rule politician Sir Horace Plunkett and George Count Plunkett, Papal Count and Republican politician, father of Joseph Plunkett, executed for his part in the 1916 Rising.His mother was a cousin of Sir Richard Burton, and he inherited from her considerable height, being 6'4". The Countess of Fingall, wife of Dunsany's cousin, the Earl of Fingall, wrote a best-selling account of the life of the aristocracy in Ireland in the late 19th century and early 20th century called Seventy Years Young.Plunkett's only grown sibling, a younger brother, from whom he was estranged from about 1916, for reasons not fully clear but connected to his mother's will, was the noted British naval officer Sir Reginald Drax. Another younger brother died in infancy.Edward Plunkett grew up at the family properties, notably Dunstall Priory in Shoreham, Kent, and Dunsany Castle in County Meath, but also family homes such as in London. His schooling was at Cheam, Eton College and the Royal Military College, Sandhurst, which he entered in 1896.