The earthwork itself is a univallate rath, meaning it has a single enclosing bank rather than the multiple concentric rings found at more elaborate sites. That bank, encircling a sub-circular interior about 29 metres across, still stands to a reasonable 1.1 to 1.2 metres along its eastern half. The western half, however, has been replaced entirely by modern stone walls, so the monument presents a kind of split personality, half-ancient earthen bank, half-pragmatic farm boundary.

Inside, and detectable through the dense overgrowth despite everything working against inspection, are the ruins of a small stone hut positioned a little north-west of centre. The structure is modest, a circular area of about 4 metres in diameter enclosed by a low, grass-covered bank of collapsed walling, somewhere between 0.2 and 0.3 metres high and roughly 1.4 metres wide. Ringforts of this kind are associated with early medieval settlement in Ireland, typically dated between the fifth and tenth centuries, and internal structures like this stone hut are a common enough feature, representing the domestic or agricultural buildings that once occupied the enclosed space. What makes Knockglass Beg quietly striking is how thoroughly the layers of use have compressed here: an early medieval farmstead enclosed by an earthen bank, later colonised by modern stonework, and now serving a purpose that makes close examination both difficult and inadvisable.