Six Nations is demographically the largest First Nations reserve in Canada. As of the end of 2017, it has a total of 27,276 members, 12,848 of whom live on the reserve. These nations are the Mohawk, Cayuga, Onondaga, Oneida, Seneca and Tuscarora. Some Lenape live in the territory as well.

Seneca is the language of the Seneca people, one of the Six Nations of the Hodinöhsö꞉niʼ ; it is an Iroquoian language, spoken at the time of contact in the western part of New York. While the name Seneca, attested as early as the seventeenth century, is of obscure origins, the endonym Onödowáʼga꞉ translates to "those of the big hill." About 10,000 Seneca live in the United States and Canada, primarily on reservations in western New York, with others living in Oklahoma and near Brantford, Ontario. As of 2022, an active language revitalization program is underway.