The Prince of Wales's Leinster Regiment (Royal Canadians) was an infantry regiment of the line in the British Army, formed in 1881 by the amalgamation of the 100th (Prince of Wales's Royal Canadian) Regiment of Foot and the 109th Regiment of Foot (Bombay Infantry). The 100th Foot was first raised in 1858 and the 109th was first raised in 1853. Between the time of its formation and Irish independence, it was one of eight Irish regiments raised largely in Ireland, with its Birr Barracks home depot in Birr. It was disbanded with the Partition of Ireland following establishment of the independent Irish Free State in 1922 when the five regiments that had their traditional recruiting grounds in the counties of the new state were disbanded.

Birr is a town in County Offaly, Ireland. Between 1620 and 1899 it was called Parsonstown, after the Parsons family who were local landowners and hereditary Earls of Rosse.