Amherst Island is an island in Lake Ontario near Kingston, Ontario. The island is approximately 70 km² in size, being 20 km long and 7 km at its widest. It is part of Loyalist Township in Lennox and Addington County.

A ferry service connects the village of Stella on the island with Millhaven on the mainland.

The resident population of about 400 people doubles during the summer months. The island is also home to approximately 500 White-tailed Deer. In the winter, Snowy Owls regularly visit the island. The island is home to Long-eared Owls and Great Horned Owls in summer.

The island was known by the French as Isle Tonti, after Henri de Tonty , who accompanied La Salle during his explorations. The island was later settled by United Empire Loyalists and renamed Amherst Island in 1792 after Jeffrey Amherst, 1st Baron Amherst, who was commander-in-chief of British forces in North America.