||This article relies largely or entirely upon a single source. (August 2009)
The De Mercy family rose to increasing power during the Middle Ages in the region of what is now southern Belgium, Lorraine and Luxembourg.
By the fifteenth century Jean de Mercy was lord of Clémarais (1422); in 1477, Roger de Mercy ("the Valiant") was appointed Captain and Provost of Longwy by Duke René II of Lorraine. The family progressively expanded their domain, incorporating parts of Aix-sur-Cloie, Battincourt and Piémont. A castle named Claimaraix is mentioned in a document dated 3 March 1612, as a possession of Anne de Landres, widow of Jean de Mercy. By the sixteenth century they owned substantial land near Esch, including the castle at Mittenthal and the important mill at Bergem.
The inheritance of Count Claudius Florimund de Mercy (1666-1734), Imperial field marshal, (born at Longwy in Lorraine) passed to the Counts d'Argenteau.
Important scions of the family 
- Florimond Claude, comte de Mercy-Argenteau (1727–1794), Austrian diplomat, son of Antoine, comte de Mercy-Argenteau, who arranged the marriage of Louis XVI to Marie Antoinette.
- Marie-Charles-Isidore de Mercy, 1736-1811, Bishop of Luçon 1775-1801; Archbishop of Bourges, 1802-1811
- Eugène Arnould Henri Charles François Marie, comte de Mercy-Argenteau (22 Aug. 1838-2 May 1888). Husband of the musician Marie-Clotilde-Elisabeth Louise de Riquet, comtesse de Mercy-Argenteau, a collaborator with Franz Liszt.