Knocklegan, or Knockaliagain as it appears in older records, translates roughly as the hill of the standing stone, which means the stone was significant enough, long enough ago, to anchor a place-name that has outlasted almost everything else about its history. The stone itself leans against a field wall or ditch, a posture that might suggest neglect but may simply be how it has always sat, a large unworked column of rock that has been marking this particular hill for longer than anyone can reliably say.

The Ordnance Survey Letters of 1839, in which surveyors and their correspondents recorded vernacular and antiquarian detail across Ireland as part of the great mapping project of that era, give precise dimensions: seven and a half feet above ground, nearly three feet wide at the base, tapering to one and a half feet at the top, and a foot through in thickness. A later description by O'Kelly, writing in 1969, uses the Irish term liagán, meaning a long upright stone or column, and notes that it is uncarved and uninscribed, with no ogham lettering or decorative work of any kind. Standing stones of this type are among the most common and least understood prehistoric monuments in Ireland. They may have marked boundaries, burial sites, astronomical alignments, or routes across the landscape, and without associated finds or excavation most remain stubbornly unclassifiable. This one offers no additional clues. It is, in the most literal sense, a stone on a hill, which is also what the townland has been called for centuries.