Isabella Montagu, Duchess of Manchester (c. 1706 – 20 December 1786), formerly Lady Isabella Montagu, was the wife of William Montagu, 2nd Duke of Manchester. She was the daughter of John Montagu, 2nd Duke of Montagu, and his wife, the former Lady Mary Churchill. Her sister, Mary, became Countess of Cardigan. Their three brothers all died in childhood. She married the Duke of Manchester on 16 April 1723, about two years after he had inherited the dukedom. They were childless, and remained married until the Duke's death in 1739. There were two children from this second marriage: