The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Illinois
    n 1: a midwestern state in north-central United States [syn:
         Illinois, 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