Measuring roughly 20 metres from northeast to southwest and 16 metres from northwest to southeast, this fortified enclosure was built to surround Derrydonnell Castle, maintaining a careful distance of about 3 metres from the castle walls on all sides. Constructed from roughly coursed mortared rubble, the bawn walls stand between 2.5 and 3 metres high with a thickness of approximately 1 metre, though time and agricultural activities have taken their toll on the structure.

The defensive capabilities of this bawn become apparent in its corner bastions and gun loops, features that transformed it from a simple enclosure into a formidable fortification. Angle bastions are positioned at the eastern and western corners, each containing five gun loops that would have allowed defenders to cover approaching threats with overlapping fields of fire. Two additional gun loops can be found near the western bastion; one in the southwest wall and another in the northwest wall, ensuring comprehensive coverage of the surrounding landscape. These military features reflect the uncertain times in which the bawn was constructed, when local landowners needed to defend their holdings against potential raids and conflicts.

While much of the southeast, southwest and northwest walls survived in reasonable condition according to surveys from the late 20th century, the structure has suffered various damages over time. The northeast side experienced significant collapse where a later building was constructed against it, whilst sections of the southern end of the southwest wall and the middle of the southeast wall have also fallen. Unfortunately, land improvement works before 2005 caused further damage to the southwest wall. Interestingly, this smaller bawn connects to a larger outer bawn that extends from its northwest side, suggesting a complex defensive system that evolved over time to meet changing security needs at Derrydonnell.