The northern pier at Slade is roughly sixty metres long and four to five metres wide, but its construction tells a story in two distinct phases, one built partly by cutting directly into the limestone bedrock and using the quarried blocks to form the pier itself, and a later raising of the surface with smaller stones, along with a new shelter wall built on top of the original. Three corbels, short stone brackets projecting from the pier's northern face, belong to that second phase of building, along with the stump of a fourth. What is quietly puzzling is that an 1839 Ordnance Survey map shows the pier at roughly half its current length, yet there is no visible break or seam in the stonework to indicate where any extension might have begun.

The pier's origins lie in 1684, when Henry Loftus built a quay here for fishing boats, as recorded by a contemporary observer named Robert Leigh. The Loftus family had held land at Slade since at least 1666, when Nicholas Loftus was confirmed in possession of 157 acres. In 1685, Henry leased the property to Henry Mansel, a man with a colourful recent past: he had been implicated in the Monmouth Rebellion, the failed Protestant uprising against the Catholic King James II of England that same year. Mansel put the pier to commercial use, importing rock salt and coal to supply the saltworks he developed nearby. Saltworks of this period typically involved evaporating brine to extract salt, a labour-intensive industrial process that required a reliable supply of raw materials by sea. By 1746 the pier was recorded as being in need of repair, and it remained, in one form or another, Slade's only pier until 1847, when a second pier was constructed to the east as part of a famine relief scheme, one of the many public works projects across Ireland intended to provide wages to those devastated by the Great Famine. The facing along the southern side of the harbour, in front of the old castles and the saltworks site, appears to date from the same mid-nineteenth-century campaign of works, its stonework closely resembling that of the 1847 pier.