Earl of Mornington is a title in the Peerage of Ireland. It was created in 1760 for the Anglo-Irish politician and composer Garret Wellesley, 2nd Baron Mornington. On the death of the fifth earl in 1863, it passed to the Duke of Wellington; since that date, the title has generally been used by courtesy for the heir apparent to the heir apparent to the dukedom.

The Peerage of Ireland consists of those titles of nobility created by the English monarchs in their capacity as Lord or King of Ireland, or later by monarchs of the United Kingdom of Great Britain and Ireland. It is one of the five divisions of Peerages in the United Kingdom. The creation of such titles came to an end in the 19th century. The ranks of the Irish peerage are duke, marquess, earl, viscount and baron. As of 2016, there were 135 titles in the Peerage of Ireland extant: two dukedoms, ten marquessates, 43 earldoms, 28 viscountcies, and 52 baronies. However, these titles have no official recognition in the Republic of Ireland, with Article 40.2 of the Constitution of Ireland forbidding the state conferring titles of nobility and stating that an Irish citizen may not accept titles of nobility or honour except with the prior approval of the Irish government.