Exhibit 21.1 Significant Subsidiaries of Dynegy Inc. As of December 31, 2002 SUBSIDIARY STATE OF INCORPORATION 1. Dynegy Holdings Inc. Delaware 2. Illinova Corporation Illinois 3. Dynegy Marketing and Trade Colorado 4. Dynegy Power Marketing, Inc. Texas 5. Illinois Power Company Illinois 6. NNG Holding Company, Inc. Delaware 7. Dynegy Northeast Generation, Inc. Delaware 8. Dynegy Midwest Generation, Inc. Illinois 9. Dynegy Catlin Member Delaware