This Irish classic, which is better known in this country by its phonetic form Killian, is one of several newer recommended Gaelic choices that have entered the American name pool. Killian now stands at Number 516 in the US, while Cillian is 22 in its Irish homeland.
There are several Saint Cillians, including one who was sent to Bavaria to convert the natives and was martyred for his trouble. The best known contemporary bearer of the name in versatile actor Cillian Murphy.
Patrick Woulfe, a Catholic priest who was instrumental in reviving native Irish names in that country after the war for independence from England in the 1920s, theorized that Cillian might also be related to a Gaelic name meaning war.