| SFSeneca Foods CORP | Princeville | IL | Food Manufacturing311421 | 100-499 | ◐ LIKELY ACTIVE |
| SFSensient Flavors INC | Amboy | IL | Food Manufacturing311920 | 100-499 | ◐ LIKELY ACTIVE |
Service Filtration CORP | Northbrook | IL | Machinery Manufacturing333914 | 100-499 | ◐ LIKELY ACTIVE |
| SOSeymour of Sycamore | Sycamore | IL | Printing and Related Support Activities323111 | 100-499 | ◐ LIKELY ACTIVE |
| SMSheet Metal Werks, Inc. | Arlington Heights | IL | Fabricated Metal Product Manufacturing332322 | 20-99 | ◐ LIKELY ACTIVE |
| SSignode-bridgeview | Bridgeview | IL | Fabricated Metal Product Manufacturing332999 | — | ◐ LIKELY ACTIVE |
| SCSika CORP | Aurora | IL | Chemical Manufacturing325998 | — | ◐ LIKELY ACTIVE |
| SASlidematic Acquisition, LLC | Chicago | IL | Fabricated Metal Product Manufacturing332710 | — | ◐ LIKELY ACTIVE |
| SISouthern Illinois Storm Shelters INC | Benton | IL | Plastics and Rubber Products Manufacturing326199 | — | ◐ LIKELY ACTIVE |
| SSSparrer Sausage | Chicago | IL | Food Manufacturing311612 | — | ◐ LIKELY ACTIVE |
Sparrow Millwright of Laharpe, INC | La Harpe | IL | Machinery Manufacturing333992 | — | ◐ LIKELY ACTIVE |
| SCSpectrulite Consortium Incorporated | Madison | IL | Primary Metal Manufacturing331315 | — | ◐ LIKELY ACTIVE |
| SISpringfield INC | Geneseo | IL | Fabricated Metal Product Manufacturing332994 | 100-499 | ◐ LIKELY ACTIVE |
Steel-guard Safety CORP | South Holland | IL | Miscellaneous Manufacturing339999 | 1-19 | ◐ LIKELY ACTIVE |
| SCStepan Company | Elwood | IL | Chemical Manufacturing325194 | — | ◐ LIKELY ACTIVE |
Sun Chemical CORP | Northlake | IL | Chemical Manufacturing325910 | — | ◐ LIKELY ACTIVE |
Sun Chemical CORP | St Charles | IL | Chemical Manufacturing325910 | — | ◐ LIKELY ACTIVE |
Sun Chemical CORP | Kankakee | IL | Chemical Manufacturing325910 | — | ◐ LIKELY ACTIVE |
Swan Analytical Usa, INC. | Wheeling | IL | Computer and Electronic Product Manufacturing334516 | 20-99 | ◐ LIKELY ACTIVE |
| SISwd INC | Addison | IL | Fabricated Metal Product Manufacturing332812 | 100-499 | ◐ LIKELY ACTIVE |
| SFSynergy Flavors INC | Wauconda | IL | Food Manufacturing311930 | 100-499 | ◐ LIKELY ACTIVE |
| SFSynergy Flavors Innova LLC | Chicago | IL | Food Manufacturing311612 | — | ◐ LIKELY ACTIVE |
| TPTakeda Pharmaceuticals | Round Lake | IL | Chemical Manufacturing325412 | 500+ | ◐ LIKELY ACTIVE |
| TLTate & Lyle Solutions USA LLC | Hoffman Estates | IL | Food Manufacturing311221 | 500+ | ◐ LIKELY ACTIVE |
| TCTaylor Co- Division of Carrier Commercial Refrigeration INC | Rockton | IL | Machinery Manufacturing333241 | — | ◐ LIKELY ACTIVE |
| TDT & D Metal Products | Watseka | IL | Primary Metal Manufacturing331221 | 100-499 | ◐ LIKELY ACTIVE |
| TCTechalloy CO INC | Union | IL | Primary Metal Manufacturing331110 | — | ◐ LIKELY ACTIVE |
Technics Fabrication INC | Bolingbrook | IL | Machinery Manufacturing333914 | — | ◐ LIKELY ACTIVE |
| TATechnotrans America INC | Mount Prospect | IL | Machinery Manufacturing333415 | 20-99 | ◐ LIKELY ACTIVE |
| THThe Hallstar Company | Chicago | IL | Chemical Manufacturing325199 | — | ◐ LIKELY ACTIVE |
| TRThe Rdi Group General Partnership | Itasca | IL | Machinery Manufacturing333120 | 100-499 | ◐ LIKELY ACTIVE |
Thermal Care INC | Niles | IL | Machinery Manufacturing333415 | — | ◐ LIKELY ACTIVE |
| TITitan Industries, Inc. | Deer Creek | IL | Fabricated Metal Product Manufacturing332312 | 20-99 | ◐ LIKELY ACTIVE |
| TCToledo Concrete INC | Toledo | IL | Nonmetallic Mineral Product Manufacturing327320 | 1-19 | ◐ LIKELY ACTIVE |
| TPTransworld Plastic Films, INC. | Rochelle | IL | Miscellaneous Manufacturing339999 | 20-99 | ◐ LIKELY ACTIVE |
| TPTriangle Package Machinery Company | Chicago | IL | Machinery Manufacturing333993 | 100-499 | ◐ LIKELY ACTIVE |
| TRTrim Rite Food CORP | Carpentersville | IL | Food Manufacturing311612 | — | ◐ LIKELY ACTIVE |
| UIUltratech Inc | Dupage | IL | Fabricated Metal Product Manufacturing332322 | 20-99 | ◐ LIKELY ACTIVE |
| UIUniphase, Inc. | St. Charles | IL | Plastics and Rubber Products Manufacturing326199 | 20-99 | ◐ LIKELY ACTIVE |
| ULUnited Laboratories, Inc. | St. Charles | IL | Chemical Manufacturing325612 | 100-499 | ◐ LIKELY ACTIVE |
| UPUniversal Packaging Corporation | Centralia | IL | Paper Manufacturing322212 | — | ◐ LIKELY ACTIVE |
USA Printworks Illinois INC. | Woodstock | IL | Printing and Related Support Activities323113 | 1-19 | ◐ LIKELY ACTIVE |
| UDUS Doe Argonne National Laboratory | Argonne | IL | Miscellaneous Manufacturing339999 | — | ◐ LIKELY ACTIVE |
| VRVandalia Ready Mix | Vandalia | IL | Nonmetallic Mineral Product Manufacturing327320 | 1-19 | ◐ LIKELY ACTIVE |
| VJVegetable Juices INC | Bedford Park | IL | Food Manufacturing311411 | 20-99 | ◐ LIKELY ACTIVE |
| VCVertex Chemical CORP | Dupo | IL | Chemical Manufacturing325131 | — | ◐ LIKELY ACTIVE |
| VUVesuvius USA | Charleston | IL | Nonmetallic Mineral Product Manufacturing327120 | — | ◐ LIKELY ACTIVE |
| VSV&V Supremo Foods | Chicago | IL | Food Manufacturing311513 | 100-499 | ◐ LIKELY ACTIVE |
| WCWalnut Custom Components | Walnut | IL | Wood Product Manufacturing321992 | 20-99 | ◐ LIKELY ACTIVE |
| WPWarwick Publishing Company | Saint Charles | IL | Printing and Related Support Activities323111 | 20-99 | ◐ LIKELY ACTIVE |