The title of Conte di Magenta was created on 30 December 1619 for Don Luigi Melzi, of a Milanese patrician family.
His descendant Gaspare, eighth Count, married Maria Teresa d'Eril, daughter and heiress of the Marchese de Fuente Sagrada, and their descendants adopted the name Melzi d'Eril.
On 20 December 1807 he was created Duca di Lodi by Napoleon in his capacity as King of Italy.
The Duke was childless, and adopted as his heir his nephew Giovanni Francesco.
His son Lodovico, twelfth Count of Magenta, reassumed the title of Duca di Lodi in 1859.