Newcastle West grew up around a castle, the ruins of which are located off the town square. The large castle ruins are well maintained.
The castle was built by the FitzGerald family who arrived at some point after 1194, by 1298 the castle had been completed in stone. The town then came to be known as Newcastle, West Limerick, but over time the ‘west’ became part of Newcastle and the town was known by the current name Newcastle West.
According to Begley, the parish was called Newcastle and Ardagh in 1704. Newcastle was joined with Monagea from 1722 until 1764 when it became a separate parish. Lewis stated that parts of Monagea and Killeedy were in the parish of Newcastle West.
Two notable mentions included in the history of the diocese of Limerick were the first Monsignor in the diocese, Richard Baptist O’Brien in 1881, and Denis Hallinan who was P.P. here and later became Bishop.
Sir William Courtenay, the local landlord, held 10,500 acres (42 km2) of land in Newcastle West in the late 16th century. He was a staunch Catholic, and suffered persecution for his beliefs. His son George may have practiced his faith in secret. Their home was reputed to have had a room in which priests were hidden. William Courtenay was denounced in the House of Commons as a papist recusant in 1624.
During the reign of Elizabeth I, three battles were fought near here. Tradition has it that the locals killed many of the Knights Templar. The town was sacked in 1302 and destroyed in 1315. Two of the Earls of Desmond died here. Garrett (better known as Gearóid Iarla) in 1399, and James, the 8th earl, in 1462.
Markets were held on Tuesday, Thursday, and Saturday. Large numbers used to attend Thursday’s hiring fairs for farm workers. Fairs were held on April 1, May 3, July 12, August 20, October 1, and December 10.