Miami-Illinois (Myaamia IPA: [mjɑːmia]) is a Native American Algonquian language formerly spoken in the United States, primarily in Illinois, Missouri, Indiana, western Ohio and adjacent areas along the Mississippi River by the tribes of the Illinois Confederacy, including the Kaskaskia, Peoria, Tamaroa, Cahokia, and Mitchigamea. Since the 1990s the Miami Tribe of Oklahoma has worked to revive it in a joint project with Miami University in Oxford, Ohio.
Miami-Illinois is an Algonquian language within the larger Algic language family. The name "Miami-Illinois" is a cover term for a cluster of highly similar dialects, the primary ones being Miami proper, Peoria, Wea, Piankeshaw, and, in the older Jesuit records, Illinois. About half of the surviving several hundred speakers were displaced in the 19th century from their territories, eventually settling in northeastern Oklahoma as the Miami Nation and the Peoria Tribe. The remainder of the Miami stayed behind in northern Indiana.
The language was documented in written materials for over 200 years. Jacques Gravier, a Jesuit missionary who lived among the Kaskaskia tribe in the early 18th century, compiled an extensive and detailed Kaskaskia–French dictionary. Based on an analysis of its handwriting, it appears to have been transcribed by his assistant, Jacques Largillier.
Gravier's dictionary contained nearly 600 pages and 20,000 entries. It is the "most extensive of several manuscripts" which French missionaries made of the Illinois languages. The original document is held by Trinity College in Hartford, Connecticut. During the 18th and 19th centuries, the Illinois were subject to extermination by hostile tribes, as well as encroachment by European settlers. The French abandoned the Kaskaskia mission.
Eventually many survivors went to the Indian Territory, where the group became known as the Peoria. Others among the Illinois remained in historic territory of present-day Indiana. Because of the decline among the number of Miami-Illinois speakers, the language was not studied as extensively as some Native American families. It was not until 2002 that the manuscript was edited and published, by Carl Masthay.