The bawn itself, measuring approximately 38 metres north to south and 31 metres east to west, can still be traced through subtle scarps visible in the southern and western portions of the adjoining field. Tie-stones found towards the northern end of the castle's western wall suggest the bawn was integrated into the castle's structure, though it appears a full masonry wall may never have been completed around the entire enclosure.

The castle's position within this rectangular enclosure follows a typical Irish defensive pattern, where the main fortified building anchored one corner of a larger protected area. These bawns served as secure courtyards where livestock could be driven during raids and where daily activities could be carried out under the protection of the castle walls. The incomplete nature of Rathumney's bawn walls might indicate either economic constraints during construction or that the natural topography of the west-facing slope provided sufficient defence alongside the existing structures.

About 350 metres to the east-southeast stands the site of Rathumney church, suggesting this was once a small but complete medieval settlement. The proximity of these two structures; castle with its bawn and the church site; paints a picture of a local lord's estate where both secular and religious life intersected, a common arrangement in medieval Ireland where castle, church, and community existed in close relationship to one another.