The central feature is a rectangular grass-covered platform measuring 44.1 metres from north to south and 41.6 metres from east to west. This raised area is enclosed by earthen banks that have weathered the centuries remarkably well; their bases span 3 to 3.6 metres wide, narrowing to about a metre at the top. The banks rise between 0.5 and 0.9 metres above the interior platform, whilst on the exterior they stand between 1 metre high on the eastern side and 1.7 metres on the western edge.

Surrounding these earthworks are the remnants of what were once water-filled moats or fosses, though most have now filled in over time. Only the western moat retains its original form, with a top width of 3.2 metres narrowing to 2 metres at the base and reaching a depth of 0.7 metres. These defensive ditches would have provided both protection and drainage for the site, a common feature of medieval settlements and fortifications across Ireland.

The banks show numerous gaps where the earth has given way over the centuries, making it impossible to identify the original entrance point. Such moated sites typically date from the Anglo-Norman period through to the late medieval era, when they served as defended homesteads for wealthy landowners or minor nobility. The substantial earthworks at Carrownalassan suggest this was once a place of some local importance, though its exact history remains lost to time.