The original priory once occupied a plot now threaded through by Circular Road, and the only physical acknowledgement of its existence is a commemorative plaque near the entrance to the house. By the early 19th century, when the Ordnance Survey recorded the area, no standing fabric remained at all. What the surveyors could still identify was a rectangular patch of ground, roughly 22 metres by 16, labelled simply as the Cemetery of St John's, tucked between Circular Road and Dublin Road.

The foundation was attributed to Turloch O'Conor, who established it around 1140 as a priory or hospital dedicated to St John the Evangelist. It appears to have adopted Arroasian observance shortly afterwards, meaning it followed the rule associated with Augustinian canons, a reform movement that spread widely across Ireland in the 12th century. By around 1304, a contemporary source described it as lying in the suburbs of Tuam, which gives a sense of how the town's boundaries have shifted over the centuries. The institution grew in status, becoming an abbey around 1360, and continued in some form of use until at least 1574. James Morris's 1720 map of Tuam still depicted an L-shaped building aligned roughly north to south, so the structure survived in some recognisable form well into the early modern period before disappearing entirely. A further trace of the site's significance emerged when the head of a high cross was found close by, suggesting the area had considerable ecclesiastical weight long before the priory itself was founded.