Knockabbey Castle and Gardens reflect the constantly changing fortunes of its owners for more than six centuries. The numerous additions and changes evident in the castle and gardens are like different chapters in a book; all telling different stories about different periods and people.

When it was first built in 1399, it was called Thomastown Castle and consisted only of a simple square building; the tower house where the interpretative centre is now housed. This structure offered its owners, the Bellews, comfort and security at a time when skirmishes between the native Irish and the New English and Norman settlers were quite common.

Reflecting their prestige and position, the Bellews extended the tower house to the west around 1650. That extension with its original stairwell and its elegant six-bayed facade still exists today.

The Bellew family fortunes changed when Roger Bellew supported the deposed Catholic King James II against King William of England. Following William's victory over James's troops at the Battle of the Boyne, Bellew's estate was confiscated and mortgaged to a new owner.