No trace of the mills survives above ground, and their precise locations have never been established. What remains is a paper trail through civic records and one brief glimpse underground, enough to sketch the outline of an industrial operation that once sat at the edge of a functioning hospital precinct and outlasted it by decades.

The three mills, known collectively as St John's Mills, belonged to the Hospital of Saint John the Baptist, a religious house that stood outside the New Gate on the west side of medieval Dublin. The watercourse that powered them ran along what was then called Saint Thomas Street, and its route is marked on John Speed's 1610 map of the city, with the mills indicated by an X between St. Catherine's Church and John's Lane West. The documentary record is unusually detailed. In 1457 the Dublin Assembly Roll recorded the city granting Saint John's House the course of the water as they had held it of old, at forty shillings a year, with the warning that if the rent went unpaid, a plumber named John Staines would receive the water instead for forty years. A year later, in 1458, the Dublin White Book set out the terms of a forty-year lease between the Mayor and the Prior of the hospital, specifying the water's path from a small structure called le watyrhouse near Crokkers Gate, its passage through the hospital grounds, and the city's retained right to divert it into the city ditch in times of need. After the Dissolution of the Monasteries, a 1540 survey noted that while the church had been demolished and its materials sold off by William Brabazon, under-treasurer of Ireland, the three watermills were specifically excluded from the grant made to Edmund Redman, leased instead to a Nicholas Benet at a rent of 220 pecks of wheat and malt. In 1564 the Assembly Roll recorded Alderman Christopher Sedgrave receiving the watercourse for a term of sixty-one years, still at the familiar forty shillings a year.

In 1995, archaeologist Linzi Simpson excavated a section of the medieval watercourse beneath the north-east corner of what is now the National College of Art and Design, on the south side of Oliver Bond Street. That building, and the surrounding streetscape, is the closest a visitor can get to the site today. There is nothing to see at ground level, but standing on Oliver Bond Street or along John Street, with Speed's 1610 map in mind, gives some sense of how a managed watercourse once threaded through this densely occupied part of the city, doing industrial work for an institution that has otherwise entirely disappeared.