The Derry flows under Clonegal Bridge
|Origin||Hacketstown, County Carlow|
|Mouth||Irish Sea at Wexford as the River Slaney|
South of Tinahely it turns sharply and flows southwest through Shillelagh, briefly forming the border between County Wicklow and County Wexford, before becoming the border between County Wexford and County Carlow.
A few kilometers further downstream it flows into the River Slaney.
Derry Water River is a separate tributary, which rises near Tinahely and flows north-eastwards to form the Aughrim River.