Trefoil Island is an island with an area of 115.79 ha, in south-eastern Australia. It is part of Tasmania’s Trefoil Island Group, lying close to Cape Grim, Tasmania’s most north-westerly point, in Bass Strait. It is owned by the Trefoil Island Aboriginal Cooperative and is home to an estimated 1.5 million breeding pairs of short-tailed shearwaters, which are subject to annual muttonbirding activities.