Kilian is the German and French spelling of the Irish Cillian, from the Gaelic ceall, "church", so it is usually explained as "little church" or "bright-headed". Saint Kilian, an Irish missionary martyred in Würzburg in the 7th century, made the name a Franconian classic, and actor Cillian Murphy has brought the Irish form to American ears. In the United States Kilian ranked number 3711 in 2000, peaked at number 1032 in 2023 and stands at number 1167 in 2025.