Fort William Augustus, Fort and national historic site on Grassy Island, Canso, Canada

Fort William Augustus stands on Grassy Island off Canso, where remains of the 1720 redoubt, the 1723–24 fort, and the 1735 blockhouse are still visible. The site was recognized as a National Historic Site of Canada in 1962.

New Englanders began building Fort William Augustus on Grassy Island in 1720, during the lead-up to Father Rale's War; the permanent structure broke long-standing Mi'kmaq–British American agreements. On 7 August 1720, 60–75 Mi'kmaq and French fishermen from Petit de Grats attacked the unfinished fort, killing three men and wounding four. A twelve-gun blockhouse followed the 1723 raid, and the French and Mi'kmaq destroyed the fort in the 1744 Raid on Canso during King George's War.

The fort's name honours Prince William, Duke of Cumberland, son of George II. The site is also called Fort Phillips after Governor Richard Philipps, and Grassy Island Fort after its location. The 1720 construction broke long-standing agreements between the Mi'kmaq and British Americans, a grievance that fed into Father Rale's War.

Access to the fort requires a boat from the mainland since it sits on an island. The Parks Canada visitor center in Canso provides information and exhibits to help you understand the site's history and archaeological findings.

The fort was first called Fort Phillips, after Governor Richard Philipps, and was also known as Grassy Island Fort. It was named William Augustus after Prince William, Duke of Cumberland, son of George II. On the site remain traces of the 1720 redoubt, the 1723–24 fort and the 1735 blockhouse.