The titles of Marquess De Grey and Earl De Grey were created in the peerages of Great Britain and the United Kingdom respectively for descendants of the Greys, Duke of Kent and Earls of Kent, created 1465, who were unrelated or extremely distantly related to the family of the Earls Grey created 1806.
Henry Grey, 12th Earl, 1st Marquess and 1st Duke of Kent, and Baron Lucas of Crudwell, was created Marquess De Grey in 1740. As this title had a special remainder, it did not become extinct on his death later that year, along with some of his other titles, but passed to his granddaughter, who therefore became 2nd Marchioness De Grey, Jemima (née Campbell), Countess of Hardwicke, who was the daughter of Lady Amabel Grey by her husband the 3rd Earl of Breadalbane. The title of Marquess De Grey became extinct on her death in 1797.
The 2nd Marchioness De Grey's daughter Amabel, suo jure Baroness Lucas, was created Countess De Grey in 1816. On her death without issue, the title passed to her sister's son Thomas, 3rd Baron Grantham, who became 2nd Earl De Grey and adopted the name of "De Grey". He died in 1859, when the Earldom passed to his nephew George, 2nd Earl of Ripon (son of the Prime Minister Lord Goderich). The 2nd Earl of Ripon and 3rd Earl De Grey was created Marquess of Ripon in 1871, and was succeeded in 1909 by his son Frederick, who became 4th Earl De Grey, 3rd Earl of Ripon, 2nd Marquess of Ripon, 3rd Viscount Goderich, and 5th Baron Grantham. All the titles became extinct on his death in 1923.