Dorothy Spencer (née Sidney; later Smythe), Countess of Sunderland (5 October 1617 (baptised) – 5 February 1684), was the wife of Henry Spencer, 1st Earl of Sunderland, and the daughter of Robert Sidney, 2nd Earl of Leicester, and Lady Dorothy Percy.

In about 1635, she rejected a marriage proposal from the poet Edmund Waller, who addressed verses to her under the nickname "Sacharissa" (which he based on the Latin word sacharum, meaning "sugar").

It seems to have been a love marriage and had her family's wholehearted approval: her father after her husband's death wrote that he thanked God for the part he had played in her happiness.

[2] In 1643, Spencer was created 1st Earl of Sunderland in recognition of his service to King Charles I in the English Civil War.

[3] Spencer was killed at the First Battle of Newbury, leaving Dorothy with two children, and pregnant with a third, who died young.