The Chippewa Cession is large, roughly specified territory, spreading from the southern to the northern border of United States of America, alongside Mississippi River. It borders with Wisconsin, Illinois, Virginia, Carolina and Florida to the east and Dakota, Kansas, Louisiana and Texas to the west.
The land was ceded back to Indigenous Tribal Federations in the 1830s in return for help. That help includes work that keeps the original Salem Accord signer, Sarah Alder, alive over 300 years later. 
English and Ojibwe are widely spoken in the cession.
Witch and civilian populations seem to mingle more freely in the cession compared to other states in the United States. Due to this, some witches practice a Christo-pagan faith in the Cession that is separate from the monotheistic faith practiced by most witches in the rest of the country.
Comparisons to the Real World
According to the map from the opening of the show, its takes up what would have been the states of Minnesota, Iowa, Missouri, Arkansas, and Louisiana.