Marquessate of Ailsa
Arms of Kennedy, Marquesses of Ailsa: Argent, a Chevron Gules, between three crosses-Crosslet fitchée Sable, the whole within a Double-Tressure flory counterflory of the second. Crest: A Dolphin naiant proper. Supporters: On either side, a Swan wings inverted proper, beaked and membered Gules[1]
Creation date	10 September 1831
Created by	King William IV
Peerage	Peerage of the United Kingdom
First holder	Archibald Kennedy, 1st Marquess of Ailsa
Present holder	David Kennedy, 9th Marquess of Ailsa
Heir apparent	Archibald Kennedy, Earl of Cassilis
Remainder to	The 1st Marquess' heirs male of the body lawfully begotten
Subsidiary titles	Earl of Cassilis Lord Kennedy Baron Ailsa
Status	Extant
Former seat(s)	Culzean Castle Cassillis House
Motto	AVISE LA FIN (Consider the end) [1]

Marquess of Ailsa, of the Isle of Ailsa in the County of Ayr, is a title in the Peerage of the United Kingdom. It was created on 10 September 1831 for Archibald Kennedy, 12th Earl of Cassilis.^[2][3] The title Earl of Cassilis (pronounced "Cassels") had been created in 1509 for the 3rd Lord Kennedy. This title had been created in the Peerage of Scotland in 1457. The 1st Marquess had been created Baron Ailsa in the Peerage of the United Kingdom on 12 November 1806.^[4][3]

The name of the title was taken from the Island of Ailsa Craig in the Firth of Clyde.^[5]

James Kennedy, Archbishop of St Andrews, was the younger brother of the first Lord Kennedy.

The Marquess of Ailsa is the hereditary Clan Chief of Clan Kennedy.

The family's seats were Cassillis House^[6] and Culzean Castle, near Maybole, Ayrshire.

• Gilbert Kennedy, 1st Lord Kennedy (c. 1406–c. 1480)
• John Kennedy, 2nd Lord Kennedy (died 1508)
• David Kennedy, 3rd Lord Kennedy (died 1513) (created Earl of Cassilis in 1509)

• David Kennedy, 1st Earl of Cassilis (1463–1513)
• Gilbert Kennedy, 2nd Earl of Cassilis (died 1527)
• Gilbert Kennedy, 3rd Earl of Cassilis (1515–1558)
• Gilbert Kennedy, 4th Earl of Cassilis (c. 1541–1576)
• John Kennedy, 5th Earl of Cassilis (c. 1573–1615)
• John Kennedy, 6th Earl of Cassilis (died 1668)
• John Kennedy, 7th Earl of Cassilis (1653–1701)
• John Kennedy, 8th Earl of Cassilis (1700–1759)

From 1759 to 1762 the titles and estates were in dispute between the heir male and the heir general. The latter, William [Douglas], Earl of Ruglen and March later Duke of Queensberry, was son and heir of William [Douglas], Earl of March, by his wife Anne [Hamilton], suo jure Countess of Ruglen, 1st dau. and heir of line of John [Hamilton], Earl of Selkirk and Ruglen, by his first wife Lady Anne Kennedy, the only daughter that had issue of John [Kennedy], 7th Earl of Cassillis. He claimed the estates under an entail of 5 September 1698, which he contended could not be set aside by the entail of 1759. The entail of 1759 was however upheld, though by a narrow majority, in the Court of Session, and confirmed, on appeal, by the House of Lords. He then, under the designation of "William, Earl of Cassillis, Ruglen and March" claimed "the titles and honours of Earl of Cassillis and Lord Kennedy," on the ground of certain charters of 24 April 1641 and 29 September 1642. Sir Thomas Kennedy, Bart., claimed the said titles as heir male, and the two petitions having been laid before the House of Lords, it was adjudged, 27 January 1762, that the latter had a right "to the honour and dignity of Earl of Cassillis as heir male of the body of David, the 1st Earl of Cassillis, and [to that] of Lord Kennedy as heir male of the body of Gilbert, the 1st Lord Kennedy."^[7]

• Thomas Kennedy, 9th Earl of Cassilis (died 1775), previously the 4th Baronet of Culzean
• David Kennedy, 10th Earl of Cassilis (died 1792)
• Archibald Kennedy, 11th Earl of Cassilis (died 1794)
• Archibald Kennedy, 12th Earl of Cassilis (1770–1846) (created Baron Ailsa in 1806 and Marquess of Ailsa in 1831)

• Archibald Kennedy, 1st Marquess of Ailsa (1770–1846)
• Archibald Kennedy, 2nd Marquess of Ailsa (1816–1870)
• Archibald Kennedy, 3rd Marquess of Ailsa (1847–1938)
• Archibald Kennedy, 4th Marquess of Ailsa (1872–1943)
• Charles Kennedy, 5th Marquess of Ailsa (1875–1956)
• Angus Kennedy, 6th Marquess of Ailsa (1882–1957)
• Archibald David Kennedy, 7th Marquess of Ailsa (1925–1994)
• Archibald Angus Charles Kennedy, 8th Marquess of Ailsa (1956–2015)^[8][9]
• David Thomas Kennedy, 9th Marquess of Ailsa (b. 1958)^[8][9]

• Cokayne, George E. (1910). Gibbs, Vicary (ed.). The complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct, or dormant. Vol. I, Ab-Adam to Basing. London: St. Catherine Press. pp. 67–68.
• Leigh Rayment's Peerage Pages ^{[self-published source] [better source needed]}
• The Rulers of Strathspey, a history of the lairds of Grant and the Earls of Seafield, 1911, by the Earl of Cassilis

• Cokayne, George E. (1998). Hammond, Peter W. (ed.). The complete peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, extant, extinct, or dormant. Vol. XIV, Addenda and Corrigenda. London: St. Catherine Press. pp. 12–13.
• Hesilrige, Arthur G. M. (1921). Debrett's Peerage and Titles of courtesy. London, UK: Dean & son, limited. p. 29.