The Earldom of Castlemaine was a title created 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,...

. It was created for Roger Palmer

Roger Palmer, 1st Earl of Castlemaine

Roger Palmer, 1st Earl of Castlemaine PC was an English courtier, diplomat, and politician who sat in the House of Commons in 1660. He was also a noted Catholic writer...

, the husband of Barbara Palmer

Barbara Palmer, 1st Duchess of Cleveland

Barbara Palmer, 1st Duchess of Cleveland was an English courtesan and perhaps the most notorious of the many mistresses of King Charles II of England, by whom she had five children, all of which were acknowledged and subsequently ennobled...

 (née Villiers), mistress to King Charles II

Charles II of England

Charles II was monarch of the three kingdoms of England, Scotland, and Ireland.Charles II's father, King Charles I, was executed at Whitehall on 30 January 1649, at the climax of the English Civil War...

. The Earl was also given the title Baron Limerick.

The title was limited to his male heirs by Barbara (i.e. as opposed, that is, to any later wife he might have) making it clear that the Earldom was for his wife's services to the King and not his own. As the only child officially fathered by the 1st Earl (which probably was not actually his) was a female, the title became extinct on his death.

Earls of Castlemaine, First Creation (1661)

• Roger Palmer, 1st Earl of Castlemaine
  Roger Palmer, 1st Earl of Castlemaine
  Roger Palmer, 1st Earl of Castlemaine PC was an English courtier, diplomat, and politician who sat in the House of Commons in 1660. He was also a noted Catholic writer...
  
  (1634–1705)