The site first appears on the Down Survey map of Mullingar Parish as a tower house, a type of fortified residence common in medieval Ireland. In 1641, these lands belonged to Thomas Petit, identified in the survey as an ‘Irish papist’, marking him as a Catholic landowner during a particularly turbulent period of Irish history. By the time the Ordnance Survey mapped the area in 1837, the castle had been reduced to a collection of small buildings and plots bisected by a laneway, though the name Castlemitchel persisted.

Today, visitors to the site will find an impressive earthwork rather than stone walls and towers. The castle’s bawn, or fortified enclosure, survives as a substantial square earthwork measuring roughly 140 metres east to west and 135 metres north to south. This defensive perimeter consists of an inner earthen bank, some 4 to 8 metres wide, with a fosse (defensive ditch) and sections of an outer bank. The fortifications are best preserved along the eastern and southern sides, where a double bank with an intervening fosse can still be traced amongst the tree line. The wide fosse remains particularly visible from the southeast corner round to the west, whilst the outer bank, rising up to 2 metres high in places, is most prominent from the southeast to the south-southwest.

Archaeological surveys have revealed tantalising glimpses of the castle’s original structures. Low wall footings in the northeast quadrant likely mark the location of the castle building itself, whilst the stony foundation of the old laneway that once bisected the site can still be traced on the ground. Though the two rectangular buildings shown on the 1913 Ordnance Survey map have vanished without trace, and a modern farm shed now intrudes on the earthwork’s eastern edge, the site retains its essential character as a medieval stronghold. Recognised for its historical importance, Castlemitchel was added to the Register of Historic Monuments in April 1989, ensuring its preservation as a window into County Westmeath’s fortified past.