Jane Spencer-Churchill, Duchess of Marlborough (29 March 1798 – 12 October 1844), formerly Lady Jane Stewart, was the first wife of George Spencer-Churchill, 6th Duke of Marlborough.
She married the duke, then Marquess of Blandford, on 13 January 1819.
It was the future duke's first legal marriage, though he had previously gone through a false marriage ceremony (with his brother, Lord Charles Spencer-Churchill, playing the role of clergyman) and had then lived as husband and wife in Scotland with the 16-year-old Susannah Adelaide Law, which might have made the marriage legal under Scottish law.
Blandford had successfully contested the matter in court, even though she had a child by him.
His mother was obliged to pay Susannah an allowance in order to prevent her making public his letters.