English River 66 is a First Nations reserve[3] in Cochrane District, Ontario, Canada, located adjacent to the settlement of Mammamattawa and just downstream of the mouth of the Kabinakagami River at the Kenogami River.

[1][4][5] It is one of two reserves of the Constance Lake First Nation, and has an area of 3,108 hectares (7,680 acres).

[3] A Hudson's Bay Company trading post was established in 1884 at the confluence of the Kenogami and Kabinakagami Rivers.

[6] It was known as the English River Post, as the Kenogami was also known as the English River.

[2] The English River First Nation, the primary forerunner to today's Constance Lake First Nation, had a reserve set aside for their use just north of the post in 1912, which remains part of the Constance Lake First Nations lands as English River 66 Indian Reserve.