[Facts] Re: My column on Sean (and Shawn and Shaun)
Something that many people don't realize is that the vast majority of Irish people had ordinary English names for centuries because of how much control the English had over Ireland. From what I've read, Irish people in the 19th century spoke English and had English names. Irish names weren't revived until the late 19th/early 20th century due to Irish nationalism, which led to a revival of Gaelic culture.
The first American-born Seans were probably the children of recent Irish immigrants. During the 1920s many Irish were still leaving Ireland.
Needless to say, some English names were more common in Ireland than the rest of the English-speaking world due to Ireland being mostly Catholic. But I think these tended to be saint names (such as Patrick, Ignatius, Theresa, and Ursula) rather than Gaelic names.