Copyright © 2013, updated 2019 Jane E. Wilcox, Forget-Me-Not Ancestry, Albany, NY www.4getmenotancestry.com.
In the early 2000s I researched the origins of surnames in England and of the surname Wilcockson in particular to include in a chapter of my book on the origins of Puritan William Wilcockson of Biggin by Hulland, Derbyshire, and his wife Margaret probably Harvie of Ilkeston, Derbyshire who immigrated to New England in 1635. The following is my research for that chapter as prepared in 2013, with DNA evidence added in 2019, debunking the Welsh nobility origins myth that was presented by Thomas Wilcox in his two 20th century genealogies and showing that the surname Wilcockson in England is polygenetic.
Adding Y-DNA evidence to the picture, we find that the surname Wilcockson is indeed polygenetic. Many Wilcox and Wilcockson (and other variations) men whose roots can be traced to England have tested for Y-DNA. Y-DNA is passed from father to son to son and so on through the male line. Based on the results shown on the Wilcox DNA Project page, we see a few clusters of Wilcockson-descended testers who have been grouped into different clusters based on their Y-signatures. This means that the men who originated the hereditary Wilcockson surname in England in the 1300s or 1400s for that particular lineage were not related in genealogically-relevant times.
For example, I have concluded that the origins of Puritan William Wilcockson of Stratford, Connecticut in 1635 were in Biggin by Hulland, Derbyshire, with a probable father named William Wilcockson, a tanner. This conclusion is based on traditional genealogical research and Y-DNA results. William’s descendants all share the same Y-DNA signature within the R-M269 haplogroup. The Wilcockson surname in Biggin appears first in the Duchy of Lancaster court rolls in November 1440. A 1415 survey of landholders in Biggin (called Coucher’s survey) has no Wilcocksons on the list. It’s possible the Wilcocksons from elsewhere moved into Biggin by Hulland between 1415 and 1440, or one of the men there took on the hereditary surname within that time while he lived in Biggin. The surname Wilson was included in the Coucher survey. It’s even possible that Wilson in Biggin morphed into Wilcockson.
Then there are the Wilcocksons who lived in Crich Parish at Over Holloway and Wheatcroft, Derbyshire in the 1500s and 1600s. Descendants of Robert Wilcockson of Crich born ca. 1640 also fall into the R-M269 haplogroup, but they have a different Y signature from the Biggin Wilcocksons. This means that for these Wilcocksons, their Wilcockson surname originated independently from the Biggin Wilcockson surname with a different man.
Finally there are the Wilcoxons who lived in Maryland in the 1700s. Their haplogroup is R-M198, a separate haplogroup from the Biggin and Crich Wilcocksons. No matter where this line originated in England, the Y-DNA haplogroup clearly shows a separate origin for this line with the surname Wilcoxon.
These are only three examples of the hereditary surname Wilcockson originating at three different locations in England before the mid-1500s with the lineages having three different Y-DNA signatures. The surname Wilcockson is polygenetic.
In conclusion, given what we know about the formation of surnames, the theories springing from William a.k.a. Wilkok of Wales are highly dubious—a great story, but highly dubious. Instead, the DNA evidence shows that the surname Wilcockson was polygenetic—that it sprang from several sources in several different locations in England–and apparently it was used first in northern England in the 1200s and 1300s. I would also say that the surname originated as a diminutive or endearment for William so that it became Wilcocks–and the -son was added later to make Wilcockson.
 Family Tree DNA, the testing company that does the Y-DNA test, matches testers based on how closely they are related to each other. Lisa Wilcox, administrator of the Wilcox DNA Project, groups the testers who join the project based on these results for the Wilcox DNA Project page.
 Duchy of Lancaster Court Rolls 1440-1441, DL 30/34/343, National Archives, England.
 Duchy of Lancaster Coucher Survey of Biggin 1415, DL 424, National Archives, England.
 Alan Wilcockson, unpublished research.
 Shannon Wilcoxon Green, unpublished research.Posted on by Jane Wilcox