 The name of the township has been traced back to Rostrevor, a seaside community in County Down, now in Northern Ireland.It is known that some of the early settlers, such as the McClains, came from County Down so it is surmised that they probably named their new community out of affection for the native village and spelled it phonetically as Rostraver Unfortunately, they neglected to leave to posterity any record of having done so.According to the United States Census Bureau, the township has a total area of 32.9 square miles (85.2 km²), of which 32.2 square miles (83.4 km²) is land and 0.7 square miles (1.8 km²; 2.13%) is water.