St. John's Well survived centuries of devotion, official disapproval, and at least one parliamentary resolution against it, only to be finished off by the mundane pressures of Victorian urban development. What remains is almost nothing: a contested patch of ground, and the knowledge that something genuinely old was once here.

The well's history reaches back further than its familiar dedication suggests. According to the antiquarian Archdall, writing in 1786, it was originally dedicated to St. Maighnain, and it was the Knights Hospitallers of Kilmainham, the medieval military-religious order whose priory gave the area its Irish name, Cill Mhaighneann, who rededicated it to St. John. A pattern, the traditional Irish custom of prayer, communal gathering, and sometimes festivity held on a saint's feast day, was observed here each year on the 24th of June. By 1538, the well was prominent enough that Dr. Staples, Bishop of Meath, preached at it. By 1710, the Irish House of Commons had passed a resolution declaring the devotion a menace. The pattern had, by then, acquired the character of a fair, with tents and booths erected for the occasion, drawing what one contemporary described as a mixed class of patrons. The drunkenness and disorder that followed made it a recurring problem for clergy and civic authorities alike. In 1818, a ferry service was maintained near Steeven's Lane for a full week each year specifically to carry north-side Dubliners across the Liffey to attend. By July 1834, police reports were recording its effective suppression, achieved with the agreement of the landowner.

The well's precise location shifted over time, or at least the memory of it did. Joyce, writing in the early twentieth century, placed its original site roughly one hundred and twenty yards downhill from where O'Connell Road crosses the railway line, in the direction of the Phoenix Park. It was later moved into a niche in the wall on the western side of the road, and then swept away entirely during construction of St. John's Terrace and the railway. A flat stone slab in a waste plot near the terrace was thought to mark the more recent site. Folklorist Caoimhín Ó Danachair, writing in 1958, suggested that an iron hatch cover on the west side of Islandbridge Road, opposite Bully's Acre, might indicate where it once stood. That hatch cover, if it still exists, is about as close to the well as anyone is likely to get now.