Origin of the Name "Whitlock"
Some of the oldest references to the name occur in the Domesday Book. This survey was done by William the Conqueror in 1086 and is essentially a financial accounting of what William had won at the Battle of Hastings. It listed each estate in the country, who controlled it in 1066 and also in 1086, listing the revenue it contributed in 1066 compared to 1086. There are eight different references to Wihtlac in the Domesday book, all in Hampshire. While technically not a surname as it is only a one word name, it could be the origin of what evolved into a surname. (Wihtlac was definitely Saxon as his holdings in 1086 had dropped significantly from what he held in 1066.)
The transition to surnames took place fairly quickly. By 1100 the records show about 45% of persons recorded, both humble as well as great, Saxon as well as Norman have surnames. By 1200 this figure is at least 90% and by 1300 it is 99% The early records may be a bit misleading as relatively few persons of humble circumstances appear in the records. While it is rare by 1300 to find a person without a surname it is debatable whether the person understood what the clerk had written down or whether the next generation used the same name.
The name Whitlock is definitely Saxon in origin and there is no question the "Whit" portion means "White". The controversy surrounds the meaning of the "Lock" section of the name. The common assumption is "White Hair". While the simplest explanation is normally the correct one I also like the explanation that "Lock" is a section of something or an enclosure. An enclosed section of a stream is a "lock" and enclosed body of water is a "loch". As the name arises in the major chalk areas of Britain, Wiltshire, Devon, Cumberland etc. I like the possibility that it means "White" "Enclosure". The Whitlocks were persons who built white enclosures out of chalk for their family or animals.