The title of Duke of Montagu has been created several times. It was first created in the Peerage of England

Peerage of England

The Peerage of England comprises all peerages created in the Kingdom of England before the Act of Union in 1707. In that year, the Peerages of England and Scotland were replaced by one Peerage of Great Britain....

 in 1705 for Ralph Montagu, 3rd Baron Montagu of Boughton

Ralph Montagu, 1st Duke of Montagu

Ralph Montagu, 1st Duke of Montagu was an English courtier and diplomat.-Life:He was the second son of Edward Montagu, 2nd Baron Montagu of Boughton and Anne Winwood, daughter of the Secretary of State Ralph Winwood...

, with the subsidiary title Marquess of Monthermer, but became extinct in 1749. The first Duke had been created Earl of Montagu and Viscount Monthermer in 1689. The Dukedom was then recreated in the Peerage of Great Britain

Peerage of Great Britain

The Peerage of Great Britain comprises all extant peerages created in the Kingdom of Great Britain after the Act of Union 1707 but before the Act of Union 1800...

 in 1766 for the late Duke's son-in-law, George Montagu (né Brudenell), 4th Earl of Cardigan

George Montagu, 1st Duke of Montagu

George Montagu, 1st Duke of Montagu, KG PC, FRS was a British peer.He was born George Brudenell in 1712 at Cardigan House, Lincoln's Inn Fields, in London, the son of the 3rd Earl of Cardigan and his wife, the former Lady Elizabeth Bruce...

, with the subsidiary title Marquess of Monthermer. On his death in 1790 the dukedom and marquessate became extinct, and the earldom passed to his brother, James Brudenell, 5th Earl of Cardigan

James Brudenell, 5th Earl of Cardigan

James Brudenell, 5th Earl of Cardigan held several offices in the Parliament of Great Britain and in service to the King of Great Britain....

. The dukedom is named for the ancient Anglo-Norman

Anglo-Norman

The Anglo-Normans were mainly the descendants of the Normans who ruled England following the Norman conquest by William the Conqueror in 1066. A small number of Normans were already settled in England prior to the conquest...

 family rather than any place.

Earls of Montagu (1689)

Other titles: Baron Montagu of Boughton (1621)

• Ralph Montagu, 3rd Baron Montagu of Boughton, 1st Earl of Montagu
  Ralph Montagu, 1st Duke of Montagu
  Ralph Montagu, 1st Duke of Montagu was an English courtier and diplomat.-Life:He was the second son of Edward Montagu, 2nd Baron Montagu of Boughton and Anne Winwood, daughter of the Secretary of State Ralph Winwood...
  
   (1638–c. 1709) was created Duke of Montagu in 1689

Dukes of Montagu, first Creation (1705)

Other titles: Earl of Montagu (1621) and Baron Montagu of Boughton (1621)

• Ralph Montagu, 1st Duke of Montagu
  Ralph Montagu, 1st Duke of Montagu
  Ralph Montagu, 1st Duke of Montagu was an English courtier and diplomat.-Life:He was the second son of Edward Montagu, 2nd Baron Montagu of Boughton and Anne Winwood, daughter of the Secretary of State Ralph Winwood...
  
   (1638–c. 1709) was a courtier and diplomat
• John Montagu, 2nd Duke of Montagu
  John Montagu, 2nd Duke of Montagu
  John Montagu, 2nd Duke of Montagu, KG, KB, PC , styled Viscount Monthermer until 1705 and Marquess of Monthermer between 1705 and 1709, was a British peer...
  
   (1690–1749), only son of the 1st Duke, died without male issue

Dukes of Montagu, second Creation (1766)

Other titles: Marquess of Monthermer (1766), Earl of Cardigan (1661), Baron Brudenell of Stonton, in the county of Leicester (1628) and Baron Montagu of Boughton, in the county Northampton (1786)

• George Montagu, 1st Duke of Montagu
  George Montagu, 1st Duke of Montagu
  George Montagu, 1st Duke of Montagu, KG PC, FRS was a British peer.He was born George Brudenell in 1712 at Cardigan House, Lincoln's Inn Fields, in London, the son of the 3rd Earl of Cardigan and his wife, the former Lady Elizabeth Bruce...
  
   (1712–1790), son-in-law of the late 2nd Duke
• John Montagu, Marquess of Monthermer
  John Montagu, Marquess of Monthermer
  John Montagu, Marquess of Monthermer was a British peer.He was born John Brudenell, eldest son of George Brudenell, 4th Earl of Cardigan by his wife Mary, daughter of John Montagu, 2nd Duke of Montagu...
  
  (1735–1770), only son of the 1st Duke, predeceased his father unmarried