The parish is in the barony of Tulla. It is 5 miles (8.0 km) northwest of Killaloe on the road to Scarriff. It lies on the south side of Scariff bay, which opens into Lough Derg. Most of the parish lies in a valley, with high hills in the background. The parish covers 5,554 acres (2,248 ha). Most of the land is suitable for farming, but there is some mountain bog. As of 1837 there was the ruins of an old church at Ballybrohan, and the ruins of Cahir castle on a small island about 100 yards (91 m) from the shore. The castle had recently been partially blown up after having been used for illegal distillation.
The parish of Ogonnelloe is in the Roman Catholic Diocese of Killaloe. Churches are St Mary's in Ballybrohan and St Molua's in Ogonnelloe.Townlands are Aughinish, Ballybran, Ballybroghan, Ballyheefy, Ballyhurly, Ballylaghnan, Ballynagleragh, Bealkelly (Eyre), Bealkelly (Purdon), Caher, Carrowcore, Carrowena, Carrowgar, Islandcosgry, Rahena Beg and Rahena More.