Source : Webster's Revised Unabridged Dictionary (1913)

Illinois \Il`li*nois"\, n.sing. & pl. (Ethnol.)
   A tribe of North American Indians, which formerly occupied
   the region between the Wabash and Mississippi rivers.

Source : WordNet®

Illinois
     n 1: a Midwest state in north-central United States [syn: {Prairie
          State}, {Land of Lincoln}, {IL}]
     2: a member of the Algonquian people formerly of Illinois and
        regions to the west
     3: the Algonquian language of the Illinois and Miami peoples