 He was acclaimed a saint in the early 11th century, during the reign of the High King of Ireland Máel Sechnaill mac Domnaill but was already listed as a saint in the earlier 9th century martyrologies compiled by Óengus of Tallaght.A medieval poem entitled "On the breaking up of a School" composed by Tadhg Og O Huiginn, c.1400, refers to the death of Dallán which caused his school to break up and the students to disperse as they would accept no other master.In a list of ancient Irish authors contained in the Book of Ballymote, Dallán is called "grandson of testimony".