Perhaps, in searching for the family history of the Irish Stevens line, it might help to take a step back and look at the broad overview of Irish surnames in general. For such a tactic as that, there is no better place to visit than the website of Irish researcher John Grenham.
After some of the details I had gleaned last week, I was beginning to wonder whether Stevens might not even be an Irish surname. It was encouraging to pull up John Grenham's map of Stevens households in mid-nineteenth century Ireland. Details used in this map were gleaned from the mid-century Griffith's Valuation.
Thankfully, I spotted one lone Stevens household showing for County Mayo, the location claimed by John Stevens as his origin on his Declaration of Intent after arrival in Indiana. In addition, there were a few Stevens households in other locations in the northern regions of Ireland—and far more households listed under the Stephens spelling variation.
Still, I wasn't sure whether Stevens was truly an Irish surname. Thankfully, John Grenham had answers. According to his sources—mostly, in this case, the volumes by Edward MacLysaght, Irish Families and More Irish Families—he noted that all Gaelic names began with "O'" or "Mac."
How a name like Stevens would fit into a picture of history like that is not yet clear to me. And that can only mean one thing: keep digging further for the answer.