Ballygrennan Castle is a ruined medieval tower house located near Askeaton in County Limerick, Ireland. It is believed to have been built in the late 15th century by the Fitzgerald family, the powerful Earls of Desmond who dominated much of Munster during the medieval period. The castle formed part of a network of fortified residences and defensive sites controlled by the Desmond Geraldines, who used such structures to protect their lands and maintain authority over the surrounding countryside. Its position near fertile farmland and important local routes would have made it a valuable stronghold within the Desmond lordship.
During the 16th century the power of the Desmond earls declined following the Desmond Rebellions (1569–1583), a series of uprisings against English rule in Munster. After the defeat and death of Gerald FitzGerald, 15th Earl of Desmond in 1583, many Geraldine castles across the region were confiscated, damaged, or abandoned during the subsequent Munster Plantation, when English settlers were granted confiscated lands. Ballygrennan Castle appears to have gradually fallen out of use during this period, like many smaller tower houses that were no longer strategically important.
