Isabella Molyneux, Countess of Sefton, formerly Viscountess Molyneux, (née Lady Isabella Stanhope; c. 1748 – 29 January 1819) was a British peeress and society figure.

Lady Isabella Stanhope was the second child of William Stanhope, 2nd Earl of Harrington and Lady Caroline FitzRoy, a daughter of Charles FitzRoy, 2nd Duke of Grafton.

[5][6] She was painted by notable painters including Catherine Read and Thomas Gainsborough, and engraved by the artist James Watson.

[7][8] A portrait of her by Gainsborough was unveiled at the inaugural exhibit of the Royal Academy of Art.

A poem written in 1768 by Temple Luttrell, son of Simon Luttrell, 1st Earl of Carhampton, titled Ode to Lady Isabella Stanshope on Her Birthday, was dedicated to her.