The Mattock River is a river in Ireland. It is a tributary of the River Boyne. 
Its source is near Collon (), from where it flows through County Louth towards the southeast until a place west of Drummond Tower in Coolfore where it begins to form the boundary between Counties Meath and Louth. Here it turns towards the southwest until Monknewtown where it takes a southeastern direction again before turning roughly east at Dowth. It joins the River Boyne at Oldbridge in the parish of Drogheda (). The estimated terrain elevation above sea level is 10 metres.
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