|Earldom of Loudoun|
|Peerage||Peerage of Scotland|
|First holder||John Campbell, 2nd Lord Campbell of Loudoun|
|Present holder||Simon Michael Abney-Hastings, 15th Earl of Loudoun|
|Heir presumptive||Hon. Marcus William Abney-Hastings|
|Subsidiary titles||Lord Campbell of Loudoun|
Lord Tarrinzean and Mauchline
Earl of Loudoun (pronounced "loud-on" //), named after Loudoun in Ayrshire, is a title in the Peerage of Scotland. It was created in 1633 for John Campbell, 2nd Lord Campbell of Loudoun, along with the subsidiary title Lord Tarrinzean and Mauchline. The 1st Earl's wife Margaret was the granddaughter and heiress of Hugh Campbell, who had been created Lord Campbell of Loudoun; he resigned the peerage in favour of his grandson-in-law, who was later created an earl.
The 6th Countess married the 2nd Earl of Moira, who was later created Marquess of Hastings. The next three Earls also held that Marquessate. However, with the death of the 4th Marquess, the Marquessate became extinct, but the Earldom passed to the elder daughter of the 2nd Marquess.
The heir apparent to the Earldom uses the courtesy title Lord Mauchline.
The heir presumptive is the present holder's brother, the Hon. Marcus William Abney-Hastings (b. 1981).