Heron Island is a coral cay located near the Tropic of Capricorn in the southern Great Barrier Reef, 80 kilometres north-east of Gladstone, Queensland, Australia, and 460 km (290 mi) north-north-west of the state capital Brisbane. The island is situated on the leeward (western) side of Heron Reef, a fringing platform reef of significant biodiversity, supporting around 900 of the 1,500 fish species and 72% of the coral species found on the Great Barrier Reef. During the summer months Heron Island is also home to over 200,000 birds including Noddy Terns and Mutton Birds.

A cay, also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic, and Indian oceans, including in the Caribbean and on the Great Barrier Reef and Belize Barrier Reef.