The bawn at Knockkelly is a fortified enclosure measuring 67 metres north to south and 75 metres east to west, its limestone rubble walls rising between six and seven metres high. Built with carefully cut corner stones and a sloping base, the structure features an extensive defensive system including gun-loops positioned at regular intervals around all four walls, approximately 4.7 metres above ground level. These would have been accessed from a wall-walk that once ran along the interior perimeter. The defences are further enhanced by the remains of bartizans at the northeast and southwest corners, whilst proper angle towers project from the southeast and northwest corners, each bristling with multiple gun-loops at ground and first floor levels.

The original entrance to the bawn was through a gatehouse positioned midway along the southern wall, though this was later incorporated into an 18th or 19th-century house that used the existing bawn wall as its frontage. According to historical records from the Ordnance Survey Letters, this gatehouse featured an arched entrance, now blocked, and the remnants of what was described as a ‘century box’ on top. Various modifications over the centuries have added new entrances; an arched gateway was inserted into the eastern wall during the 18th or early 19th century, whilst the current main entrance is through a breach in the southern wall created at a later date.

Within this formidable enclosure sits Knockkelly Castle itself, positioned off-centre in the northeast quadrant. The bawn walls contain several interesting features that speak to daily life within the fortification, including a small garderobe built into a niche in the wall near the northwest tower, complete with its original chute visible externally, and a slop-stone projecting from the wall that would have been used for disposing of waste water. The sheer number of gun-loops throughout the structure, combined with the sophisticated defensive layout, suggests this bawn was built during a particularly turbulent period when such extensive fortifications were deemed necessary for the protection of the castle and its inhabitants.