The problem is that nobody has been able to find it. The well's association with Hugh O'Neill places it at the edges of a story that is well documented in other respects, which makes its absence from the landscape all the more curious.

In 1600, O'Neill, the Earl of Tyrone and the leading force behind the Nine Years' War against English rule, marched with an army into Fearcall, the territory historically controlled by the Molloy family in what is now County Offaly. According to the Annals of the Four Masters, a seventeenth-century chronicle compiled by Franciscan scholars drawing on earlier Irish records, he stayed nine days, received the submission of the local people, and then moved on across the Slieve Bloom Mountains. It was a moment of alliance-building during a period when O'Neill was attempting to consolidate Gaelic resistance across Ulster and the midlands. Somewhere in that nine-day stay, a spring well in Glenletter apparently acquired his name, or his memory, or both. Whether it was a place he camped near, drank from, or simply passed by is not recorded.

What survives is essentially a gap. The well is listed, the chronicle entry is specific, but the physical feature itself has not been located. It joins a quiet category of Irish places that exist more securely in text than in terrain.