The first Baron of Dunsany was Sir Christopher Plunkett, second son of Christopher Plunkett, 1st Baron Killeen. The elder Christopher married Joan Cusack, heiress of Killeen and Dunsany and passed Killeen to his eldest son and Dunsany to the second. The date at which Christopher Plunkett became a peer, and an hereditary member of the Irish Parliament, is uncertain; according to Cokayne's Complete Peerage, there is no record of a Dunsany as a peer before 1489, and the creation may well have been as late as 1462, the year Sir Christopher died. On the other hand, Debrett's listed the date of creation of the peerage as 1439 (by writ; the Complete Peerage denies that peerages by writ exist in Ireland), confirmed by Letters Patent in 1461.
The first Lord Dunsany's great-great-great-great-great-great-great-great-grandson, the eleventh Baron, was a follower of King James II and was outlawed after the Glorious Revolution. He was, however, restored to his estates after the Treaty of Limerick, but neglected the necessary measures needed to have himself recognised as the holder of the peerage, and, as such, was not summoned to Parliament.
His son, the twelfth Baron, conformed to the Church of Ireland, but also did not take the necessary steps to confirm his right to the title and to the seat in the Irish House of Lords it bestowed. His son, the thirteenth Baron, however, did go through the necessary procedures to have his title and claim to a seat in the former Irish upper house admitted, and thus sat in that august body as a peer as of proven right. He was succeeded by his son, the fourteenth Baron, who served as Lord Lieutenant of County Meath, and also sat in the British House of Lords as an Irish Representative Peer from 1836 to 1848. His son, the fifteenth Baron, represented Drogheda in the House of Commons and was an Irish Representative Peer from 1850 to 1852. He was succeeded by his younger brother, the sixteenth Baron. He was an Admiral in the Royal Navy, and also served as an Irish Representative Peer between 1864 and 1889.
His son, the seventeenth Baron, sat as a Conservative Member of Parliament for Gloucestershire South and was an Irish Representative Peer from 1893 to 1899. His brother, Horace Plunkett was a key figure in the development of Irish agriculture and the Irish co-operative movement.
The seventeenth Baron was succeeded by his son, the eighteenth Baron. He was a well-known poet, playwright and author of short stories and novels, best known now for his short stories in the field of fantasy and his novel The King of Elfland's Daughter. His younger brother, Reginald Drax's descendants bear not only the Dunsany's surname Plunkett, but also other surnames inherited from their mother, Ernle Elizabeth Louisa Maria Grosvenor Ernle-Erle-Drax, née Ernle Elizabeth Louisa Jessica Burton (1855-1916), giving them a rare quadruple-barrelled surname of Plunkett-Ernle-Erle-Drax.
As of 2007, the title is held by the eighteenth Baron's grandson, Edward Plunkett, 20th Baron of Dunsany, who succeeded his father in 1999, and has two sons.
The title is listed in Burke's Peerage and Baronetage and Debrett's Peerage and Baronetage as Baron of Dunsany, but in The Complete Peerage as Baron Dunsany without the of. In either case, the holder of the title is called Lord Dunsany in all but the most formal contexts.
The heir apparent to the barony of Dunsany is the Honourable Randal Plunkett, the present holder's eldest son, issue of his lordship's second marriage.