The Earldom of Portarlington was created in 1785 in the Peerage of Ireland. The subsidiary titles of the Earldom are: Viscount Carlow (created 1776) and Baron Dawson (1770), both of which are in the Peerage of Ireland.

Viscounts Carlow (1776)

• William Henry Dawson, 1st Viscount Carlow (1712-1779)
• John Dawson, 2nd Viscount Carlow (1744-1798) (became Earl of Portarlington in 1785)

Earls of Portarlington (1785)

• John Dawson, 1st Earl of Portarlington (1744-1798)
• John Dawson, 2nd Earl of Portarlington (1781-1845)
• Henry John Reuben Dawson-Damer, 3rd Earl of Portarlington (1822-1889), elected a Representative Peer in 1855
• Lionel Seymour William Dawson-Damer, 4th Earl of Portarlington (1832-1892)
• George Lionel Henry Seymour Dawson-Damer, 5th Earl of Portarlington (1858-1900), elected a Representative Peer in 1896
• Lionel Arthur Henry Seymour Dawson-Damer, 6th Earl of Portarlington (1883-1959)
• George Lionel Yuill Seymour Dawson-Damer, 7th Earl of Portarlington (b. 1938)