Neylon is an anglicized version of the Irish surname Ó Nialláin. Other English language forms of the name include Nealon, O'Neylan, Nyland and Neilan. They were a sept of the Dalcassian tribe located in the kingdom of Thomond, which is now predominantly modern-day County Clare but encompassed parts of modern-day Tipperary and Limerick. Some early references to the name in this area come from references made to the completion in 1016 of a fortified dwelling overlooking Ballyalla lake, north of Ennis, which had the blessing of the ruling O'Brien family.