J.M. Barrie didn't invent the name Wendy. Ohio had one by 1828.
Every account says J.M. Barrie invented the name Wendy for Peter Pan. He didn't; he made it famous.
Barrie introduced Wendy Darling in the 1904 play Peter Pan (novelised in 1911 as Peter and Wendy). Census records carried the name earlier: working from the 1880 US and 1881 British censuses, The Straight Dope found about 20 American girls named Wendy, the earliest Wendy Gram of Ohio, born 1828. Wikipedia notes a male Captain Wendy Oxford in the English Civil War; it was also a British surname from the 17th century.
It likely comes from Welsh, on the element gwen-, “white, dazzling, holy,” kin to Gwendolen and Gwendydd. Barrie's version of the sound came from Margaret Henley, daughter of poet W. E. Henley, who called him “my friendy” and, unable to say R, “my fwendy-wendy.” She died around 1895, aged six.
Per Social Security Administration decade tables: Wendy did not reach the US top 1,000 names until the 1930s (rank 908). Then she climbed: 242 in the 1940s, 102 in the 1950s, 48 in the 1960s, peaking at 36 in the 1970s, before sliding to 135 in the 1980s and 250 in the 1990s. A name a child's lisp made, and America unmade.
Sources: – The Straight Dope, “Was the name Wendy invented for the book Peter Pan?” (https://www.straightdope.com/columns/read/2057/was-the-name-wendy-invented-for-the-book-peter-pan/) – Wikipedia, “Wendy” (https://en.wikipedia.org/wiki/Wendy) – SSA decade tables (via the Wayback Machine), names1930s.html through names1990s.html – The archived History of Wendy page, with Leslie Ellen Jones, Ph.D. (https://web.archive.org/web/20010627002022/http://www.wendy.com/wendyweb/history.html)
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