Where is the Algonquin tribe today?

There has never been an Algonquian tribe.

The second "a" in Algonquian makes it an adjective, meaning "like the Algonkin" - a small tribe who have always lived in the Ottawa valley between Ontario and Quebec.

Algonquian refers to a huge family of different but related languages spoken over a very wide area of the USA and Canada, all of them distantly related to the language spoken by the Algonkin. The Algonquians include the Cheyenne, Blackfoot and Arapaho of the Great Plains; the Illinois, Sac, Fox and Cree further east; the Ojibwa, Potawatomi and Ottawa north of the Great Lakes and the Shawnee, Delaware, Abanaki, Powhatan, Mahican, Massachusset, Nipmuc, Pennacook, Wappinger and many, many more tribes living along the east coast.