Sligo, Irish Sligeach (“Shelly River”) seaport and county seat, County Sligo, Ireland. It lies along Sligo Bay and the River Garavogue, between Lough (lake) Gill and the sea. Sligo's Roman Catholic cathedral serves the diocese of Elphin, and there is a Church of Ireland cathedral. Sligo has ruins of a castle and friary dating from the 13th century. Early in the reign of James I the town was granted a market and two annual fairs; in 1613 it was incorporated and received the privileges of a borough. The borough was disenfranchised in 1870.