| Honorific Prefix: | Her Grace |
| The Duchess of Portland | |
| Reign: | 8 November 17663 June 1794 |
| Reign-Type: | Tenure |
| Birth Date: | 27 August 1750 |
| Death Place: | London, England |
| Burial Place: | St Marylebone Parish Church |
| Father: | William Cavendish, 4th Duke of Devonshire |
| Mother: | Charlotte Boyle, 6th Baroness Clifford |
Dorothy Bentinck, Duchess of Portland (née Lady Dorothy Cavendish; 27 August 17503 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. They were parents of six children:
According to newspaper accounts, she was the mother of nine children, only four of whom were living at the time of her own death.
The duchess died at her home, Burlington House, Piccadilly, and was buried in St Marylebone Parish Church, Marylebone, London.[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)
| Escutcheon: | Quarterly 1st & 4th Azure a cross moline Argent 2nd & 3rd Sable three stags' heads cabossed Argent attired Or a crescent for difference (William Cavendish-Bentinck, 3rd Duke of Portland) impaling (William Cavendish, 4th Duke of Devonshire). |
| Supporters: | Two lions double queued the dexter Or and the sinister Sable. |
| Coronet: | Coronet of a Duke |