[2] Heapstown Cairn is located on a low hill immediately west of the River Uinshin and north of Lough Arrow, 2.1 km (1.3 mi) northwest of Ballindoon Friary.

In folk tradition it was the burial site of Ailill mac Echach Mugmedóin, brother of Niall of the Nine Hostages.

"[5] In 1837, when it was illustrated by George Petrie,[6] it stood to its full height and had a standing stone on the summit.

[7] The cairn is 57 m (187 ft) in diameter and about 10 meters high, and is composed of locally quarried chunks of limestone mixed with blocks of red sandstone.

The monument has been extensively quarried on all sides except the southeast, which probably contains an undiscovered passage grave beneath the cairn.