The River Boyne is a river in Leinster, Ireland, the course of which is about 112 kilometres long. It rises at Trinity Well, Newberry Hall, near Carbury, County Kildare, and flows towards the Northeast through County Meath to reach the Irish Sea between Mornington, County Meath, and Baltray, County Louth.
Salmon and trout can be caught in the river, which is surrounded by the Boyne Valley. It is crossed just west of Drogheda by the Boyne River Bridge, which carries the M1 motorway, and by the Boyne Viaduct, which carries the Dublin-Belfast railway line to the east. The catchment area of the River Boyne is 2,695 km².
The long term average flow rate of the River Boyne is 38.8 cubic metres per second.
Despite its short course, the Boyne has historical, archaeological and mythical connotations. The Battle of the Boyne, a major battle in Irish history, took place along the Boyne near Drogheda in 1690 during the Williamite war in Ireland. It passes through the ancient town of Trim, Trim Castle, the Hill of Tara, Navan, the Hill of Slane, Brú na Bóinne, Mellifont Abbey, and the medieval town of Drogheda.