| CICitiwaste INC | Joliet | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| COCity of Champaign | Champaign | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| COCity of Chicago | Chicago | IL | Paper Manufacturing322212 | — | ◇ UNVERIFIED |
| COCity of Lexington | Lexington | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CJC J R Processing CO | Des Plaines | IL | Chemical Manufacturing325998 | — | ◇ UNVERIFIED |
| CMClaire Manufacturing | Addison | IL | Chemical Manufacturing325998 | — | ◇ UNVERIFIED |
| CClariant | Mchenry | IL | Chemical Manufacturing325991 | — | ◇ UNVERIFIED |
| CPClariant Plastics & Coatings USA LLC | West Chicago | IL | Wood Product Manufacturing321991 | — | ◇ UNVERIFIED |
| CDClarin Div of Greenwich Industries LP | Lake Bluff | IL | Transportation Equipment Manufacturing336360 | — | ◇ UNVERIFIED |
 Clarke Mosquito Control Products INC. | Schaumburg | IL | Chemical Manufacturing325314 | — | ◇ UNVERIFIED |
| CCClear Channel Outdoor | Chicago | IL | Printing and Related Support Activities323113 | — | ◇ UNVERIFIED |
| CPClear Pack Company | Franklin Park | IL | Plastics and Rubber Products Manufacturing326199 | — | ◇ UNVERIFIED |
| CPClearwater Paper CORP | Elwood | IL | Paper Manufacturing322121 | — | ◇ UNVERIFIED |
| CIClement Industries | Bedford Park | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CCClimco Coils | Morrison | IL | Computer and Electronic Product Manufacturing334416 | — | ◇ UNVERIFIED |
| CCClimco Coils CO | Morrison | IL | Electrical Equipment, Appliance & Component Manufacturing335311 | — | ◇ UNVERIFIED |
| CEClinton Electronics CORP | Loves Park | IL | Computer and Electronic Product Manufacturing334411 | — | ◇ UNVERIFIED |
| CPClorox Products | Chicago | IL | Chemical Manufacturing325612 | — | ◇ UNVERIFIED |
| CSClorox Sales CO | Minooka | IL | Chemical Manufacturing325612 | — | ◇ UNVERIFIED |
| CMClybourn Metal Finishing CO | Chicago | IL | Fabricated Metal Product Manufacturing332813 | — | ◇ UNVERIFIED |
| CICmic INC | Skokie | IL | Chemical Manufacturing325412 | — | ◇ UNVERIFIED |
| CICmi INC | Elmhurst | IL | Printing and Related Support Activities323111 | — | ◇ UNVERIFIED |
| CGCn Group | Melrose Park | IL | Chemical Manufacturing325510 | — | ◇ UNVERIFIED |
| CSCoated Sand Solutions LLC | Rochelle | IL | Chemical Manufacturing325998 | — | ◇ UNVERIFIED |
| CACoatings Applications INC | Elk Grove Village | IL | Fabricated Metal Product Manufacturing332812 | — | ◇ UNVERIFIED |
| CTCoffman Truck Sales INC | Aurora | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CCCoke Contracting INC | Chicago | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CPColbert Packaging CORP | Lake Forest | IL | Paper Manufacturing322212 | 100-499 | ◇ UNVERIFIED |
| CCColeman Cable INC | North Chicago | IL | Primary Metal Manufacturing331420 | — | ◇ UNVERIFIED |
| CCColes County Dragway INC | Charleston | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CEColfax Envelope CORP | Buffalo Grove | IL | Paper Manufacturing322230 | — | ◇ UNVERIFIED |
| CACollins & Aikman CORP | Rantoul | IL | Transportation Equipment Manufacturing336390 | — | ◇ UNVERIFIED |
| CQColumbia Quarry CO | Columbia | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CFColumbus Foods | Chicago | IL | Petroleum and Coal Products Manufacturing324199 | — | ◇ UNVERIFIED |
| CMCombined Metals CORP | Bellwood | IL | Primary Metal Manufacturing331221 | — | ◇ UNVERIFIED |
| CSComed Streator | Streator | IL | Miscellaneous Manufacturing339999 | — | ◇ UNVERIFIED |
| CCCommercial Cleanser CO | Schiller Park | IL | Chemical Manufacturing325611 | — | ◇ UNVERIFIED |
| CFCommercial Finishes CO LTD | Elk Grove Village | IL | Fabricated Metal Product Manufacturing332812 | — | ◇ UNVERIFIED |
| CFCommercial Floor Covering | Champaign | IL | Printing and Related Support Activities323112 | — | ◇ UNVERIFIED |
| CFCommercial Forged Products | Chicago | IL | Fabricated Metal Product Manufacturing332111 | — | ◇ UNVERIFIED |
| CLCommercial Lithographers | Bensenville | IL | Printing and Related Support Activities323111 | — | ◇ UNVERIFIED |
| CPCommercial Products Group | Carol Stream | IL | Plastics and Rubber Products Manufacturing326130 | — | ◇ UNVERIFIED |
| CSCompx Securityproducts | River Grove | IL | Fabricated Metal Product Manufacturing332999 | — | ◇ UNVERIFIED |
| CFConagra Foods Packaged Foods LLC | St Elmo | IL | Food Manufacturing311999 | — | ◇ UNVERIFIED |
| CFConagra Foods Packaged Foods LLC | Mattoon | IL | Food Manufacturing311812 | — | ◇ UNVERIFIED |
| CFConagra Foods Packaged Foods, LLC | Centralia | IL | Food Manufacturing311824 | — | ◇ UNVERIFIED |
| CFConagra Foods - Rossville | Rossville | IL | Food Manufacturing311225 | — | ◇ UNVERIFIED |
| CSConcrete Specialties CO | Franklin Park | IL | Nonmetallic Mineral Product Manufacturing327390 | — | ◇ UNVERIFIED |
| CSConcrete Specialties CO Hazel Crest | Markham | IL | Nonmetallic Mineral Product Manufacturing327390 | — | ◇ UNVERIFIED |
| CSConcrete Supply LLC | Alorton | IL | Nonmetallic Mineral Product Manufacturing327320 | — | ◇ UNVERIFIED |
