Located in County Limerick, this fortified structure appears in the townland of Williamstown on the 1840 Ordnance Survey map, though later revisions place it in neighbouring Ballynagarde. The castle, also known as Ballywillin Castle, may date back to 1583, according to historical records cited by archaeologist Thomas Johnson Westropp in the early 20th century.

The castle’s documented history reveals a complex tale of ownership and occupation. In 1625, Theobald (or Tibbott) Bourke held Williamstown Castle, though notably excluding the “Geist Hall”. By 1636, his son John possessed only a room within the castle, along with the bawn and a stone house in the northern section. The Civil Survey of 1654-56 confirms that Theobald, Lord Baron of Brittas, an Irish Catholic, owned the property which featured both castle and bawn. Following the Cromwellian conquest, ownership became contested; Lord Brittas, Dr T. Arthur and others laid claim to the buildings in 1655, with Colonel Clayton and W. Matthews receiving a grant in 1666, though Dr Arthur’s daughters retained the middle storey.

By the 19th century, the castle had undergone significant changes. Fitzgerald described it simply as a tower without outworks, whilst the Croker family’s repairs and modernisation apparently obscured its medieval character so thoroughly that antiquarian John O’Donovan failed to locate it during his 1840 survey for the Ordnance Survey Letters. This transformation from medieval stronghold to modernised residence, and eventually to obscurity, reflects the broader patterns of change that swept across Ireland’s built heritage during this turbulent period.