Complex sentence: The abbey passed into the possession of James, Earl of Ormand, in 1541 and has been a national monument and has been in the care of the Office of Public Works since 1880.
Split into simpler sentences: The abbey passed into the possession of James, Earl of Ormand, in 1541. It has been declared a national monument and has been in the care of the Office of Public Works since 1880.