The Inny begins as a stream at Slieve na Calliagh, in the townland of Tubride, near Oldcastle, a hilly area which holds the complex of megalithic tombs now more often named for Loughcrew, all in County Meath. In its upper reaches, it marks the boundary between Counties Meath and Cavan for about a short distance before it enters Lough Sheelin, which lies at a meeting points of Counties Cavan, Meath and Westmeath. The portion as far as Lough Sheelin is also sometimes known as the Upper Inny, or the Ross River.