Dorothy Bentinck, Duchess of Portland (née Lady Dorothy Cavendish; 27 August 1750 – 3 June 1794) was Duchess of Portland and the wife of William Cavendish-Bentinck, 3rd Duke of Portland, the Prime Minister of Great Britain.

Dorothy Cavendish was born on 27 August 1750 to William Cavendish, 4th Duke of Devonshire, the Prime Minister of Great Britain and his wife Lady Charlotte Boyle, 6th Baroness Clifford.

On 8 November 1766, Cavendish was married to William Cavendish-Bentinck, 3rd Duke of Portland.

[4] She “died of a bowel complaint, which she had been subject to for many years, and which terminated in a mortification after a short illness.

It was at first suspected, from the violent inflammation in her bowels, that her Grace had eaten water-gruel out of a copper saucepan not properly tinned; but this suspicion is certainly erroneous, as it proved on examination.”[5] Bentinck was a great-great-great-grandmother of Queen Elizabeth II (see ancestry of Elizabeth II)