Its name comes from the Danish word for salmon, "lax", a linguistic trace pointing to Norse origins long before the Normans arrived. A castle once stood on the weir's line on the Clare bank, straddling the river in a fashion that made its jurisdictional identity similarly awkward; as the antiquarian Thomas Johnson Westropp observed in the early twentieth century, it was "assigned to County Clare" but "historically belongs to Limerick".

The fishery's early history is layered. Westropp recorded that the Laxweir fisheries date from Norse times and that they were granted to W. de Braosa in 1215, while O'Flaherty notes the weir was the property of the Bishop of Limerick during the thirteenth century. By the mid-seventeenth century it had passed to Limerick Corporation, who are recorded in the 1654 to 1656 Civil Survey as owners of "the greate Salmon weare called Laxweare in the River of Shannon", valued at £200 per year. That survey describes the weir's bounds with some precision, placing it between the lands of the Banke to the north, St Thomas's Island to the east, and the lands of Corbally to the south. The structure appears on the seventeenth-century Down Survey map of St Patrick's Parish and is annotated as "Salmon Weir" on the 1840 Ordnance Survey six-inch map, suggesting it remained a recognisable feature of the Shannon landscape across several centuries. The castle on the Clare side, known as Caslaunnacorran, was described by Westropp as retaining a corbelled bartizan, a small overhanging turret projecting from the wall, along with original window-slits, though he noted it had been defaced and altered over time.

The weir is not a site you walk up to easily; its interest now lies largely in the historical record and in aerial photography. The line of the structure, approximately 300 metres in length, was still visible on Digital Globe satellite imagery taken between 2011 and 2013, appearing as a faint ridge beneath the river's surface. Those curious about the broader landscape can approach the Corbally side of the Shannon via the north bank of Limerick city, where the river widens noticeably. The Down Survey map showing the "greate Salmon weyre" is held at the National Library of Ireland as MS 718, and is worth consulting alongside the OS six-inch map for a sense of how consistently this crossing point shaped the river's human geography.