The short answer is ... we don't know. However, there are a few legends. There is an oft repeated story that the name originated with the marriage of John Bonny and Jane Castle in Weeden around 1720. Now that we have found many earlier Bonnycastles, this appears to be unfounded. The story could be fanciful or, more logically, stem from misreading the parish records. Sometimes the clerk abbreviated the name to Bonny or spelled it Bonny-Castle, leading a modern reader to think it was a combined name. A second story tells us that the family name was "Castle" and that a pleased king pronounced that "You are a bonnie fellow, Castle. Your name shall be "Bonnycastle". A third story asserts that Bonnycastle is derived from the French name Belcastel. As mentioned elsewhere on this website, all living Bonnycastles are related and it appears that there is historically just one Bonnycastle tree. Bonnycastle Dale (1868-1936), Canadian writer, naturalist, and photographer, stated in his will that his young partner Cecil Griffiths could adopt the name Bonnycastle Dale Jr. in his writings. Charles Bonnycastle Willcox (1818 Portsea - ?) was almost certainly the illegitimate son of Charles Bonnycastle. Charles Bonnycastle Jewell (1813-1874), fifth child in a large Portsea, Hampshire family. Probably named after Charles who subsequently came to America. Olynthus Bonnycastle Trout (1851-1931). Olynthus was born in Ohio to Peter Francis Trout (1826-1856) & his wife Sarah Bennett, both from Franklin County, Virginia. Peter Francis' family was in Indiana in 1830 and Ohio by 1840. Did Olynthus' mother or father know a Bonnycastle, perhaps serving with JC Bonnycastle in the army? Is there some other explanation? In 1873, J G Holland wrote a novel entitled "Arthur Bonnicastle" which was initially serialized. Why he chose that name for the title character is unknown. Without difficulty, I have found several boys given the forenames Arthur Bonnicastle during the following decade! Their surnames are Herrell (born in Ohio), White (Wisconsin), Carr (Pittsburgh), Gardner (California), Johnson (Pittsburgh), Chadwick (Minnesota). No doubt there are others. There was an actual person with the complete name Arthur Bonnicastle (1876-1923). He was an Osage Indian, born in Oklahoma in 1876, attended the Carlisle Indian School in Pennsylvania, served with the Ninth Infantry in the Philippines and China, and became an Osage Chief. On the Indian Rolls, people were listed with an Indian name and an English name if they had one. I do not know who assigned the English names; two neighboring children are named Oscar Wild and David Copperfield. In 1884, Henry James wrote the short story Pandora which had characters named Mr. and Mrs Bonnycastle, thinly disguised aliases for Henry Adams and his wife, Marion. We don't know which, if any, Bonnycastle inspired its use. "The Two Bonnycastles: a farce in one act" was published in 1850 and widely staged. The author was an English playwright, John Maddison Morton (1811-1891). Again, the inspiration for the characters' names is unknown. What is the origin of the Bonnycastle surname?
Stray occurrences of Bonnycastle or Bonnicastle as a forename
Examples from literature