Created Duchesses of England is in Dukedoms of England.
On 29th September 1397 King Richard II [aged 30] rewarded his relations with Dukedoms, possibly for their part in downfall of Thomas of Woodstock 1st Duke of Gloucester [deceased], Thomas Beauchamp 12th Earl Warwick [aged 59] and Richard Fitzalan 9th Earl of Surrey 4th or 11th Earl of Arundel [deceased]...
His older half-brother John Holland 1st Duke Exeter [aged 45] was created 1st Duke Exeter. Elizabeth Lancaster Duchess Exeter [aged 34] by marriage Duchess Exeter.
His nephew Thomas Holland 1st Duke Surrey [aged 23] was created 1st Duke Surrey.
His first cousin once-removed Margaret [aged 77] was created 1st Duchess Norfolk - for life only. On the same day her grandson Thomas [aged 29] was also created Duke of Norfolk - see below.
His second cousin once removed Thomas Mowbray 1st Duke of Norfolk was created 1st Duke Norfolk. Elizabeth Fitzalan Duchess Norfolk [aged 31] by marriage Duchess Norfolk.
His first cousin Edward 2nd Duke of York 1st Duke Albemarle [aged 24] was created 1st Duke Albemarle. Beatrice Burgundy Countess Rutland and Cork [aged 24] by marriage Duchess Albemarle.
His illegitimate first cousin John Beaufort 1st Marquess Somerset and Dorset [aged 24] was created 1st Marquess Somerset, 1st Marquess Dorset. Margaret Holland Duchess Clarence [aged 12] by marriage Marchioness Somerset, Marchioness Dorset.
Ralph Neville 1st Earl of Westmoreland [aged 33] was created 1st Earl of Westmoreland. Joan Beaufort Countess of Westmoreland [aged 18] by marriage Countess of Westmoreland.
On 23rd May 1644 Alice Leigh 1st Duchess Dudley [aged 66] was created 1st Duchess Dudley by King Charles I of England, Scotland and Ireland [aged 43] for life. Her husband Robert Dudley [aged 69] had claimed to be the legitimate son of Robert Dudley 1st Earl of Leicester but the Star Chamber found against him. King Charles I of England, Scotland and Ireland disagreed with their verdict and, in compensation of her subsequent treatment, awarded her the Dukedom... See Patent of Creation.
In 1670 Barbara Villiers 1st Duchess of Cleveland [aged 29] was created 1st Duchess Cleveland, 1st Countess of Southampton and 1st Baroness Nonsuch by King Charles II of England Scotland and Ireland [aged 39] for having given birth to five of his illegitimate children.
On 19th August 1673 Louise Kéroualle 1st Duchess Portsmouth [aged 23] was created 1st Duchess Portsmouth, 1st Countess Fareham, 1st Baroness Petersfield by King Charles II of England Scotland and Ireland [aged 43] for life for being his mistress and for having given birth to his son Charles Lennox 1st Duke Richmond [aged 1].
On 19th March 1719 Melusine Schulenburg 1st Duchess Munster 1st Duchess Kendal [aged 51] was created 1st Duchess Kendal, 1st Countess Feversham, 1st Baroness Glastonbury.