“The great melting pot was a place to cook fried bread in, not to lose one’s identity in.”
Who speaks the language?
Language is a key component of culture, and a way to convey the specifics of said culture. For many, it’s the key component of the culture. Potawatomi is the language that was spoken in Chicagoland by the Potawatomi tribe when this area was originally settled by Europeans, and subsequently had its influence vastly scaled back.
Where did they go?
The Potawatomi were generally forced to head either west or north, due to treaties that either representatives or people claiming to be representatives of the tribe made with leaders of the United States. Most of these treaties were made under the assumption that the new Eurocentric nation had the upper hand, though both sides generally preferred nonviolence. 
Ethnologue page on the Potawatomi language