Along its course through the Irish landscape, the River Slaney passes by many ancient and historic sites. Rising in the southern Wicklow Mountains, it passes by hillforts and stone circles. The ruins of Baltinglass Abbey lie on its east bank. Several grand estate houses, Huntington Castle, Newtownbarry House, and Clobemon Hall all overlook its channel. The towns and villages that have developed at crossing points display a rich architectural heritage in their bridges and houses. Older signs of people living along the Slaney include ringforts and enclosures.
The history of the Slaney is not only seen in the sites along it, but in the objects left behind. Some of these materials were used to earn a living in more recent times, like fish spears and net sinkers. The River Slaney provided plenty of fish for locals, either to sell or eat themselves. Other objects point to an older history. A bronze axe head found on the outskirts of Bunclody town dates back to the Bronze Age, between 4,300-2,700 years ago. The axe head could have been used by a farmer to clear trees from the land or by a warrior in battle.