This medieval stronghold has quite the administrative history; in 1290, Gilbert de Clare, Earl of Gloucester, surrendered both this castle and Kilkenny Castle to the crown, only to receive them back as a regrant the following month. By 1306, the manor attached to the castle was valued at £26 6s 6d annually, a substantial sum that reflected its strategic importance in northern Ossory. The castle appears on a 1563 map of Leix and Offaly under the name ‘Balachassan’, marking its continued significance through the centuries.

The fortunes of Offerlane Castle took a dramatic turn in the early 14th century. A 1307 assessment of the Countess of Gloucester’s holdings reveals that whilst the castle estate encompassed 29 carucates and 60 acres of land, the entire property lay waste due to ongoing conflicts with the Irish. The situation had become so dire that the crown was spending £40 yearly just to maintain a garrison there, with Thomas de Cantewelle serving as constable in 1309. This border fortress, sitting on what was effectively a war frontier, never quite recovered its former prosperity, and in 1600, Teige Fitzpatrick dealt the final blow by burning it down.

Today, visitors to the site will find only fragments of this once formidable castle. The southwest section of a mural tower, constructed from rubble limestone in rough courses, still stands alongside remnants of an internal stairwell and the northeast corner tower. According to historical accounts from 1905, the castle once stood where the parish priest’s house was later built, with only pieces of the courtyard wall, a couple of broken turrets, a gateway, and a partially filled defensive ditch remaining. A modern school now occupies much of the original castle grounds, making this a site where medieval military architecture meets contemporary education.