It is one of twenty-nine medieval architectural fragments recorded at the site, and it carries the survey designation AF 17. Some of its companions have been pressed back into use, slotted into the abbey walls or laid flat as grave markers, but this particular piece simply remains where it fell, or was placed, at some point after the building it belonged to began to come apart.

Killagha Abbey itself is a rectangular structure occupying the northernmost edge of the graveyard, its north wall effectively serving as the graveyard's northern boundary. When surveyor Laurence Dunne examined the site in 2012, he found the interior of the graveyard little used and heavily overgrown, with only a single perimeter path still passable. Dunne had visited before, noting a further six fragments and twelve masons' marks, the small incised symbols that medieval craftsmen used to identify their work, during earlier visits in 2006 and 2010. Even so, the 2012 survey could not locate every fragment; the vegetation had simply swallowed too much of the ground. Of the twenty-nine fragments eventually recorded, sixteen had been reused within the fabric of the abbey walls themselves, and one had been placed as a grave marker beneath a piscina, the small stone basin used for draining water from the washing of sacred vessels. The window sill with its twin-light profile belongs to the remainder, the fragments dispersed around the south and south-east exterior of the building, remnants of architectural detail that once gave the abbey its medieval character.