Baron Sydney was a title that was created thrice in British history. The first creation came 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 1603 when Robert Sydney was made Baron Sydney, of Penshurst. He was later created Earl of Leicester

Earl of Leicester

The title Earl of Leicester was created in the 12th century in the Peerage of England , and is currently a title in the Peerage of the United Kingdom, created in 1837.-Early creations:...

. For more information on this creation, see this title. The second creation came in 1768 when Dudley Cosby

Dudley Cosby, 1st Baron Sydney

Dudley Alexander Sydney Cosby, 1st Baron Sydney , was an Irish politician and diplomat.-Background:Cosby was the son of Pole Cosby, of Stradbally, Queen's County, and Mary, daughter of Henry Dodwell...

, Minister Plenipotentiary to Denmark between 1763 and 1765, was made Baron Sydney, of Stradbally in the Queen's County, in the Peerage of Ireland

Peerage of Ireland

The Peerage of Ireland is the term used for those titles of nobility created by the English and later British monarchs of Ireland in their capacity as Lord or King of Ireland. The creation of such titles came to an end in the 19th century. The ranks of the Irish peerage are Duke, Marquess, Earl,...

. He was the grandson and namesake of Dudley Cosby, who represented the Queen's County

Queen's County (Parliament of Ireland constituency)

Queen's County was a constituency represented in the Irish House of Commons until 1800.-1692–1801:...

 in the Irish House of Commons

Irish House of Commons

The Irish House of Commons was the lower house of the Parliament of Ireland, that existed from 1297 until 1800. The upper house was the House of Lords...

, and the great-nephew of William Cosby. This creation became extinct on Lord Sydney's death in 1774. The third creation came in 1783 when Thomas Townshend

Thomas Townshend, 1st Viscount Sydney

Thomas Townshend, 1st Viscount Sydney PC , was a British politician who held several important Cabinet posts in the second half of the 18th century...

 was created Baron Sydney, of Chiselhurst in the County of Kent. He was later created Viscount Sydney

Viscount Sydney

Viscount Sydney is a title that has been created twice. The first creation came in 1689 when Henry Sydney was made Viscount Sydney, of Sheppey, in the Peerage of England. In 1694 he was created Earl of Romney. For more information on this creation, see this title...

 and his grandson was made Earl Sydney

Earl Sydney

Earl Sydney, of Scadbury in the County of Kent, was a title in the Peerage of the United Kingdom. It was created in 1874 for the Liberal politician John Townshend, 3rd Viscount Sydney. He notably served as Lord Chamberlain of the Household and as Lord Steward of the Household. On his death in 1890...

 in 1874. For more information on this creation, see the latter title.

Barons Sydney; First creation (1603)

• see the Earl of Leicester (1618 creation)
  Earl of Leicester
  The title Earl of Leicester was created in the 12th century in the Peerage of England , and is currently a title in the Peerage of the United Kingdom, created in 1837.-Early creations:...
  
  

Barons Sydney; Second creation (1768)

• Dudley Alexander Sydney Cosby, 1st Baron Sydney
  Dudley Cosby, 1st Baron Sydney
  Dudley Alexander Sydney Cosby, 1st Baron Sydney , was an Irish politician and diplomat.-Background:Cosby was the son of Pole Cosby, of Stradbally, Queen's County, and Mary, daughter of Henry Dodwell...
  
  (c. 1730–1774)