The precise location is no longer known. That uncertainty is itself the interesting part: a piece of infrastructure that was once functional and visible enough to be described in writing has since slipped out of the landscape entirely, leaving only the description behind.

The weir at Kilmainham is mentioned in 17th century sources, documented by the fisheries historian Arthur Went in his 1954 work, where he references those early accounts across a short run of pages. Went was a careful chronicler of Irish inland and estuarine fisheries, and the Kilmainham weir appears in that context as one of many such structures that once shaped the working life of the Liffey. Fish weirs were common on Irish rivers throughout the medieval and early modern periods, typically constructed from stakes, wattle, or stone, and they appear frequently in monastic records and later civic disputes over fishing rights. The Kilmainham area had a long association with the religious and administrative life of the city's western margins, which makes the presence of a managed fishery there entirely plausible, even if the weir's exact form and operator are not recorded in the surviving notes.

Because the site has not been precisely located, there is no point of access to mark on a map, and nothing survives above the waterline that can be confidently identified with it. Anyone with an interest in this kind of history might walk the riverside path near Kilmainham and consider how thoroughly a functional structure can disappear, not through any dramatic event, but simply through disuse, rebuilding, and the slow reordering of a riverbank over three or four centuries. The Liffey here is tidal in character, and the shoreline has changed considerably since the 17th century, which may account for some of the difficulty in pinning the weir down. The Went reference remains the starting point for anyone who wants to pursue the question further.