| Honorific-Prefix: | The Right Honourable |
| The Countess of Chatham | |
| Birth Name: | Hester Grenville |
| Birth Date: | 8 November 1720 |
| Birth Place: | London, England |
| Death Place: | Burton Pynsent, Somerset, England |
| Resting Place: | Westminster Abbey |
Hester Pitt, Countess of Chatham (; 8 November 1720 – 9 April 1803) was the wife of William Pitt the Elder, 1st Earl of Chatham, who was prime minister of Great Britain from 1766 to 1768.
The sister of George Grenville, who was prime minister from 1763 to 1765, she was also the mother of Prime Minister William Pitt the Younger and a niece of the noted Whig politician Richard Temple, 1st Viscount Cobham, who had served as her husband's mentor.
Chatham and Elizabeth Grenville, her sister-in-law, are the only two women in British history to have been both the wife of a prime minister and the mother of another prime minister.
Born on 8 November 1720 in London, she was the only daughter of Richard Grenville and Hester Grenville, 1st Countess Temple.
At 34, Lady Hester married Whig politician William Pitt on 16 November 1754 at her home in Argyle Street, London, by Francis Ayscough under special licence.[1] They had five children:
On 4 December 1761, she was created "Baroness Chatham", of Chatham, in the County of Kent", with remainder to her sons by William Pitt. Her husband was created Earl of Chatham in 1766.