The Earl of Loudoun is a title in the Peerage of Scotland, created in 1633. The title is associated with the title Lord Tarrinzean and Mauchline (created 1633), which is used as a courtesy title for whomever is the heir and eldest son of the Earl for the time being.

The sixth Countess of Loudoun married the first Marquess of Hastings. The surname of the holders of the title thus changed. The next three Earls also held the Marquessate. However, with the death of the fourth Marquess, the marquessate became extinct, but the earldom continued.

Earls of Loudoun (1633)

• John Campbell, 1st Earl of Loudoun
• James Campbell, 2nd Earl of Loudoun (d. 1684)
• Hugh Campbell, 3rd Earl of Loudoun (d. 1731)
• John Campbell, 4th Earl of Loudoun (1705-1782)
• James Muir Campbell, 5th Earl of Loudoun (1726-1786)
• Flora Muir Campbell, 6th Countess of Loudoun (1780-1840)
• George Hastings, 2nd Marquess of Hastings (1808-1844)
• Paulyn Hastings, 3rd Marquess of Hastings (1832-1851)
• Henry Hastings, 4th Marquess of Hastings (1842-1868)
• Edith Rawdon-Hastings, 10th Countess of Loudoun (1833-1874
• Charles Hastings Clifton, 11th Earl of Loudoun (1855-1920)
• Edith Abney-Hastings, 12th Countess of Loudoun (1883-1960)
• Barbara Huddleston Abney-Hastings, 13th Countess of Loudoun (1919-2002)
• Michael Abney-Hastings, 14th Earl of Loudoun (b. 1942)