The castle appears in historical records from 1574, when it belonged to Mac Owg and William Mac Tibbot, suggesting it played a role in the complex web of Gaelic lordships that characterised medieval Galway. By the time Ordnance Survey mapmakers arrived in 1838, they found only a ruined rectangular building measuring roughly 14 metres northwest to southeast and 10 metres across, which they dutifully marked on their detailed six-inch maps.

The castle’s decline continued through the 19th and early 20th centuries, and by 1929 even these ruins had been demolished, leaving surveyors to mark the location simply as “Site of” on their updated maps. Today, visitors to the site will find an irregular earthen mound scattered with large chunks of mortared stone walls, rising about four metres high and stretching 36 metres at its widest point. The surviving wall fragments, averaging 1.6 metres thick, hint at the castle’s once formidable structure, though they no longer form any recognisable floor plan.

Archaeological surveys suggest the mound sits in the southwest corner of what was likely a bawn, a defensive courtyard typical of Irish tower houses and castles. These fortified enclosures provided protection for cattle and residents during raids, a necessary feature in an area that saw frequent conflicts between Gaelic clans and Anglo-Norman settlers. While Ballygasty Castle has largely returned to the earth, its remains offer a tangible connection to the turbulent history of late medieval Galway, when local chieftains built these strongholds to control territory and project power across the surrounding countryside.