Deroy or De Roy is both a given name and a family surname of Norman origin.

Origin

Coat of arms of Le Roy, Normandy. Bibliothèque nationale de France.
A furore Normanorum, libera nos, Domine! THE KING OF AMIGNY... It is therefore to the seventh century that we would have to go back and delve into the furious hordes of those indomitable Norsemen, whose origins we have just outlined, to find there, in France, the mother stock of those LE ROYs we are discussing...

— Du Cluzel de Remaurin, Knight

Written interchangeably in records as: Roi, Roy, Le Roi, and Le Roy, the surname De Roy originated from the Normans, the descendants of Norse Vikings who settled in Amigny, a commune in Manche, Normandy. It derived from the Old French roy, roi (French pronunciation: [ʁwa]), meaning "king", or "the king" which was a byname used before the Norman Conquest and a personal name in the Middle Ages. The Normans, or "Northmen", after having settled in their new lands in Northern France, quickly adopted the Old French dialects of the region and would later take their language and naming practices with them to England.

Norman usage of the spelling variant Roy in written text dates back to the 12th-century Norman poet Wace in Roman de Rou, where he used both the "rei" & "roy" forms for the title of "king". Wace wrote in vernacular Old Norman (also known as Old Northern French), which is among the few records of Old Norman that remain. The Roy family is also recorded in the 12th century amongst the other family surnames of the city of Caen in Normandy.

Le Roy of Amigny (Silver, three black merlettes)

Originally, Roy may have been a regal name, either from "kingly" bearing, a position of authority, a tournament winner, or one who was in the service of the king. This reflects Norman adaptation of social or martial identifiers — a cultural inheritance from their Viking ancestry, eventually forming a family name that would be passed down.

Middle Ages

Coat of arms of the Knights Templar

Earliest references cite Guillaume de Roy (William of Roy), who was a knight of the Knights Templar and one of several knights, abbots and feudal lords (seigneur) of the Roy family in France and Switzerland. While born Guillaume Le Roy, the usage of de Roy ("of Roy"), a nobiliary particle, signified hereditary nobility. Specifically, this was a claimed connection to a lineage of knights and the lord of a fief recognized by the monarch, rather than a simple descriptive surname which was a legal requirement to be a knight of the Templars. Medieval court scribes consistently translated vernacular names into Latin. Guillaume de Roy is recorded as Guillelmus de Roy, Templar of the Diocese of Soissons, by the scribes during the Trials of the Knights Templar.

People with the given name

People with the surname

Deroy

De Roy