The western enclosure forms a rectangular area measuring 42.6 metres east to west and 32.6 metres north to south, defined by a scarped edge that rises three-quarters of a metre above the surrounding land. An external fosse, or defensive ditch, runs around this enclosure at about half a metre deep, whilst a slight counter-scarp bank adds an extra 30 centimetres of height to the outer defensive perimeter from the southeast to southwest corners.

Directly adjacent to the east lies a second rectangular enclosure, slightly smaller at 40 metres north to south and 24.5 metres east to west, with its scarped edge standing just over half a metre high. The southern sides of both enclosures align neatly, suggesting they were planned and constructed as a unified complex. The fosse of the western enclosure connects directly to the eastern side of the second enclosure, with approximately 5.7 metres separating the tops of the two scarps. A third, smaller rectangular area sits immediately north of the eastern enclosure, measuring 15 by 25 metres and defined by scarped edges to the west and north, whilst a modern field fence marks its eastern boundary.

These earthworks represent a type of medieval settlement common in Ireland from the 13th to 15th centuries, where wealthy landowners created defended homesteads surrounded by water-filled ditches. The multiple enclosures at Ballygrennan likely served different functions; the main western enclosure would have contained the principal dwelling, whilst the eastern areas may have housed agricultural buildings, livestock, or gardens. Low, irregular undulations visible to the west of the site hint at additional features that once formed part of this medieval complex, now barely discernible in the landscape but testament to the site’s former importance in the locality.