Did the Warrens descend from William The Conqueror?
No, but close! - Refer to this Family Tree for details.

William the Conqueror, Matilda of Flanders and the mystery of Gundred: William the Conqueror, Duke of Normandy and later King of England, married Matilda of Flanders who became Queen of England and bore him at least 9 children. Some Warren genealogies show Gundred (also spelled Gundrada) as the daughter of William the Conqueror. However non-Warren accounts of William's children do not show a daughter Gundred. Although daughters in those days were often mentioned only in a cursory fashion, if at all, the assumption that Gundred was an unnamed youngest daughter of William does not hold up. If she was William's youngest daugher she would have been born after son Henry (born in 1068) and daughter Adela. So if she was born about 1070 she would have been too young for her marriage to William de Warren in which she had 4 or 5 children before her death during childbirth in 1085. More likely she was born about 1050 to 1053 and certainly before 1054 when the Conqueror's first child Robert was born. She was married about 1077 after coming to England from Flanders or Normandy. She is believed to have met William de Warren in England.

So who was Gundred? Certainly she was the wife of William de Warren, Count of Warren at the time of the Conquest and later Earl of Surrey in England. Their marriage occurred after the Conquest of 1066. And certainly Gundred's mother was Matilda of Flanders who became Queen of England. But her father was not William the Conqueror (also known as "William the Bastard" as he was the illegitimate son of Robert, Duke of Normandy). She appears to be the step-daughter of the Conqueror and was older than all of his children (two of whom later became Kings of England).

Who was Gundred's father? The most consistent and logical information is that Matilda had two children by a previous relationship/marriage. Her son was Gherbod the Fleming (also spelled Gerbod) who was later made Earl of Chester by William the Conqueror and her daughter was Gundred. The father of both Gherbod and Gundred was also named Gherbod. He was also a Fleming and he appears to have held the hereitary office of Advocate of the Abbey of Saint Bertin in St. Omers. There is no evidence of what happened to Matilda's relationship/marriage to Gherbod. However William, Duke of Normandy sought her hand in marriage to bolster an alliance with Flanders at a time when he had his hands full with the King of France and the Count of Anjou. William may not have known she was married and had children while he was negotiating his marriage with her father, Baldwin V, Count of Flanders (who may have thought it wise not to mention her situation as he was eager for her to be married to William of Normandy). On the other hand, William was keenly interested in producing an heir and what better way than to marry a woman of proven fertility? By the way, Matilda was the granddaugher of Robert II, "The Pious", King of France. In this line she descended from Charlemagne, King of the Franks and Emperor of the West (742-813 A.D.). I've even seen a genealogy which shows all of Charlemagne's ancestors back to Adam. Believe what you will on that one!

In summary, Gundred was the daugher of the Queen of England, step-daughter of William the Conqueror, half-sister of the next two Kings of England and finally, wife of William de Warren and mother of the line of Warrens who came to America on the Mayflower.

William de Warren may have descended from Harold (Bluetooth) Blaatand, King of the Danes (Abt 903-981) and Alfred the Great, King of England (Abt 842-901). The direct male line of William de Warren, Earl of Warren and Surrey, only goes back three generations to Walter de St. Martin (born about 953). From that point the genealogy comes from Walter de St. Martin's wife (name unknown, born about 956) and her Danish male lineage (Herfastus/Herbastus).

Some Warren genealogies show William de Warren descending from Rollo (aka Robert) Ragnvaldsson of Norway, First Duke of Normandy who was the ancestor of William the Conqueror. This seems fanciful and only appears in Warren genealogies, not those of the Dukes of Normandy. The best information shows that the father of Walter de St. Martin's wife was a Dane named Herfastus de Crepon, also spelled Herbastus (born about 926) whose father may have been Harold Blaatand, King of Denmark. Harold Blaatand/Bluetooth brought Christianity to Denmark and unified Scandinavia. He is commonly thought to have been Denmark's greatest king. Harold Bluetooth (don't you love that name?) was also the great-grandson of Alfred the Great, King of England. Alfred, a Saxon King, is often considered England's greatest King.

Another possibility is that Herfastus was not Harold's son but rather the son of another Danish Knight named Herfastus "The Dane". This seems more likely and is reflected in the on-line family genealogy. In any event, William de Warren descended from a Danish noble (King or Knight).

As an aside, Richard I (San Peur/The Fearless) 3rd Duke of Normandy's mistress and later wife was Gunnor de Crepon. She was the daughter of (Sire) Herfastus de Crepon. Gunnor's sister married Walter de St. Martin. So, Duchess Gunnor was the aunt of the first William, Earl of Warren who was the first of our ancestors to carry the Warren name. The subsequent Dukes of Normandy all descended from Duchess Gunnor. From the 4th Duke of Normandy onward, the Warrens and the Dukes of Normandy (and Kings of England) have common ancestory from Herfastus "The Dane", however the Warrens did not descend from Rollo, First Duke of Normandy as some accounts show.