| Illini Community Hospital IL | Healthcare & Social Assistance | 0 | — | A |
| Illini State Trucking IN | Transportation & Warehousing | 0 | — | D |
| Illinois & Michigan Oil, LLC. IL | Transportation & Warehousing | 0 | — | F |
| Illinois American Water Company IL | Utilities | 0 | — | B |
| Illinois Auto Electric Co. IL | Manufacturing | 0 | — | F |
| Illinois Auto Electric Co. IN | Other Services | 0 | — | A |
| Illinois Auto Truck Company Inc IL | Wholesale Trade | 0 | — | A |
| Illinois Bone & Joint Institute IL | Healthcare & Social Assistance | 0 | — | B |
| Illinois Bulk Carrier IL | Transportation & Warehousing | 0 | — | D |
| Illinois CancerCare IL | Healthcare & Social Assistance | 0 | — | C |
| Illinois Central Railroad Company IL | Transportation & Warehousing | 4 | $109,642 | — |
| Illinois Central School Bus IA | Transportation & Warehousing | 0 | — | A |
| Illinois Central School Bus IL | Transportation & Warehousing | 0 | — | C |
| Illinois Central School Bus IN | Transportation & Warehousing | 0 | — | F |
| Illinois Central School Bus KS | Transportation & Warehousing | 0 | — | C |
| Illinois Central School Bus MO | Transportation & Warehousing | 0 | — | F |
| Illinois Central School Bus TX | Transportation & Warehousing | 0 | — | D |
| Illinois Central School Bus WI | Transportation & Warehousing | 0 | — | C |
| Illinois Civil Contractors, Inc. IL | Construction | 0 | — | D |
| Illinois College of Optometry IL | Educational Services | 1 | $57,512 | — |
| Illinois Crop Improvement Association, Inc. IL | Agriculture & Forestry | 0 | — | A |
| Illinois Department of Corrections IL | Public Administration | 0 | — | D |
| Illinois Department of Human Services IL | Healthcare & Social Assistance | 0 | — | F |
| Illinois Department of Revenue IL | Public Administration | 0 | — | A |
| Illinois Dept of Agriculture IL | Public Administration | 0 | — | A |
| Illinois Eastern Community Colleges Dist. #529 IL | Educational Services | 0 | — | B |
| Illinois Electric Works IL | Other Services | 0 | — | D |
| Illinois Engineered Products, Inc IL | Manufacturing | 0 | — | F |
| Illinois Environmental Protection Agency IL | Public Administration | 0 | — | A |
| Illinois Foundation Seeds Inc. ID | Agriculture & Forestry | 0 | — | A |
| Illinois Foundation Seeds, Inc WI | Agriculture & Forestry | 0 | — | A |
| Illinois Foundation Seeds, Inc. IL | Agriculture & Forestry | 0 | — | A |
| Illinois Foundation Seeds, Inc. (IFSI) IL | Agriculture & Forestry | 0 | — | D |
| Illinois Gas Company - Utility Safety & Design, Inc. IL | Utilities | 0 | — | A |
| Illinois Institute of Technology IL | Educational Services | 17 | $83,567 | — |
| Illinois Marine Towing IL | Manufacturing | 0 | — | A |
| ILLINOIS MUNICIPAL LEAGUE RISK MANAGEMENT ASSOC. IL | Public Administration | 0 | — | A |
| Illinois Mutual Life Insurance Company IL | Finance & Insurance | 1 | $103,314 | — |
| Illinois Oil Marketing Equipment, Inc IL | Construction | 0 | — | B |
| Illinois Piping Corporation IL | Construction | 0 | — | F |
| Illinois Power Generating Company IL | Utilities | 0 | — | D |
| ILLINOIS PUBLIC RISK FUND IL | Public Administration | 0 | — | A |
| Illinois Pulley & Gear, Inc. IL | Manufacturing | 0 | — | F |
| Illinois School Bus IL | Transportation & Warehousing | 0 | — | A |
| Illinois Secretary of State IL | Public Administration | 0 | — | B |
| Illinois Sleep Products Inc IL | Manufacturing | 0 | — | F |
| Illinois State Toll Highway Authority ID | Transportation & Warehousing | 0 | — | A |
| Illinois State Toll Highway Authority IL | Transportation & Warehousing | 0 | — | C |
| Illinois State Toll Highway Authority (FFO) IL | Transportation & Warehousing | 0 | — | F |
| Illinois State Toll Highway Authority (Roadway Lighting) IL | Transportation & Warehousing | 0 | — | F |
