Earl of Portarlington is a title in the Peerage of Ireland. It was created in 1785 for John Dawson, 2nd Viscount Carlow, who had earlier represented Portarlington in the Irish House of Commons. He was the son of William Dawson, 1st Viscount Carlow, who had represented Portarlington and Queen's County in the Irish House of Commons, and had been created Baron Dawson, of Dawson's Court in the Queen's County, in 1770, and Viscount Carlow, in the County of Carlow, in 1776. These titles were also in the Peerage of Ireland. The first Earl was succeeded by his eldest son, the second Earl. He was a Colonel in the 23rd Light Dragoons but disappeared the night before the Battle of Waterloo and thus missed the start of the battle. He then attached himself to the 18th Hussars, but after the battle was forced to resign his commission in disgrace, fell into dissipation and 'died in an obscure London slum'.

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.