Drumlins, those elongated hills of glacial debris that ripple across much of Ulster and the northern midlands, were favoured ground for early Irish settlement, offering natural drainage and visibility. This particular site belongs to a class of monument known as a rath or ringfort, a form of enclosed farmstead typically dating from the early medieval period, roughly the fifth to twelfth centuries. Thousands survive across Ireland in various states of preservation, but each one occupies its own specific, deliberate position in the landscape.

The earthwork at Killyreask measures roughly thirty metres east-northeast to west-southwest, and just over twenty-five metres north-northwest to south-southeast, giving it a slightly compressed oval plan. It is defined by an earthen bank and an outer fosse, which is a shallow ditch dug to reinforce the enclosure's boundary. A slight outer bank also survives along part of the southern and western arc, with a base width of around three metres and an internal and external height of roughly 0.9 metres each. The entrance through the inner bank faces southeast, with a gap of about 2.3 metres, though the outer bank at that point is complicated by the presence of two field banks that abut it. By 1983, the surrounding field banks that once enclosed the adjacent farmland had been removed, leaving the ringfort somewhat exposed and detached from the agricultural pattern that had grown up around it over the intervening centuries.