The sitter was the daughter of George Montagu, Earl of Halifax, and first wife of Francis, 7th Lord North and 3rd Lord Guilford, later 1st Earl of Guilford. Her son was Frederick Lord North, Prime Minister to King George III (see lot 60). Following her death in 1734, Francis North married secondly Elizabeth, Viscountess Lewisham (d. 1745; see lot 59), the widow of George Legge, Viscount Lewisham (1705-1732); and thirdly Katherine, Countess of Rockingham (d. 1766; see lot 57), widow of Lewis Watson, 2nd Earl of Rockingham (c. 1717-1745).
Lucy, Countess of Guilford was painted in three-quarter length by Sir Godfrey Kneller (sold Christie's London, 25 October 1968, lot 21) and full-length by Enoch Seeman (in a private collection). There is also an unattributed portrait of oval format in a private collection which appears to have been based on the present portrait, as she wears the same dress and plumed cap.