The alphamegalog of the cities of Illinois lists the largest city in Illinois for each letter of the alphabet. In this case, ‘largest’ is based on population within the city proper.

Aurora
Bloomington
Chicago
Decatur
Elgin
Freeport
Glenview
Hoffman Estates
Itasca
Joliet
Kankakee
Lombard
Mount Prospect
Naperville
Orland Park
Peoria
Quincy
Rockford
Springfield
Tinley Park
Urbana
Vernon Hills
Waukegan
Xenia
Yorkville
Zion