 The borough's name is derived from the Tappan tribe of Native Americans.According to the United States Census Bureau, Old Tappan borough had a total area of 4.197 square miles (10.870 km2), including 3.332 square miles (8.629 km2) of land and 0.865 square miles (2.241 km2) of water (20.62%).One of only four confluence points in New Jersey, the 41°N 74°W crossing, is in Old Tappan on watershed property owned by United Water.