Castlerea (; ) is the second largest town in County Roscommon, Republic of Ireland. It is located in the west of the county and, as of 2011, has a population of 3,055. Roughly translated from Irish, Castlerea can mean Brindled Castle (Caisleán Riabhach) or King's Castle (Caisleán Rí). The town is built on the banks of the River Suck and the River Francis, both of which are tributaries of the River Shannon.