| 21ST CENTURY SOLUTIONS, INC. | 59468871 | 1997-06-23 | Dissolved | — |
| 21ST CENTURY SPORTS, INC. | 60975175 | 2000-04-03 | Dissolved | — |
| 21ST CENTURY SPORTS, INC. | 57751924 | 1994-04-04 | Dissolved | — |
| 21ST CENTURY SPORTS, INC. | 54643721 | 1987-04-28 | Dissolved | — |
| 21ST CENTURY STAFFING, INC. | 60510466 | 1999-05-24 | Dissolved | — |
| 21ST CENTURY STRUCTURES, LLC | 00516279 | 2001-02-07 | Dissolved | NAPERVILLE |
| 21ST CENTURY SUPER STUCCO, INC. | 55478759 | 1989-04-10 | Dissolved | — |
| 21ST CENTURY SUSTAINABILITY CONSULTING, LLC | 06753957 | 2018-02-15 | Dissolved | CRYSTAL LAKE |
| 21ST CENTURY SYSTEMS, INC. | 59207199 | 1997-01-06 | Dissolved | — |
| 21ST CENTURY SYSTEMS, INC. | 58185647 | 1995-02-02 | Dissolved | — |
| 21ST CENTURY TAX SERVICES, INC. | 64567411 | 2005-11-16 | Active | — |
| 21ST CENTURY TAXI INC. | 60722609 | 1999-10-14 | Dissolved | — |
| 21ST CENTURY TECHNICAL PHILOSOPHY LLC | 04829808 | 2014-05-05 | Dissolved | MAYWOOD |
| 21ST CENTURY TECHNOLOGIES, INC. | 56088741 | 1990-08-31 | Dissolved | — |
| 21ST CENTURY TECHNOLOGIES, INC. | 62793589 | 2003-04-07 | Dissolved | — |
| 21ST CENTURY TECHNOLOGY GROUP INCORPORATED | 54297173 | 1986-06-27 | Revoked | — |
| 21ST CENTURY TECHNOLOGY SOLUTIONS, INC. | 69313221 | 2013-12-05 | Dissolved | — |
| 21ST CENTURY TELECOM NOC, INC. | 60069824 | 1998-08-04 | Merged | — |
| 21ST CENTURY TELECOM OF CHICAGO OPERATIONS, INC. | 60069808 | 1998-08-04 | Merged | — |
| 21ST CENTURY TELECOM OF ILLINOIS, INC. | 59607243 | 1997-10-02 | Merged | — |
| 21ST CENTURY TELECOM SERVICES, INC. | 60069832 | 1998-08-04 | Revoked | — |
| 21ST CENTURY TELEMEDICINE, LTD. | 69228232 | 2013-10-23 | Dissolved | — |
| 21ST CENTURY TITLE INCORPORATED | 61087664 | 2000-05-23 | Dissolved | — |
| 21ST CENTURY TOOLKIT, LLC | 06950108 | 2018-04-30 | Active | PARK RIDGE |
| 21ST CENTURY TRADING CORP. | 59201794 | 1997-01-03 | Dissolved | — |
| 21ST CENTURY TRANSPORT INC. | 70962144 | 2016-10-03 | Dissolved | — |
| 21ST CENTURY TRANSPORTATION, INC. | 61928286 | 2001-12-03 | Dissolved | — |
| 21ST CENTURY TRAVEL PROFESSIONALS, LLC | 00509124 | 2001-01-22 | Dissolved | CHICAGO |
| 21ST CENTURY TRAVEL, INC. | 57056789 | 1992-11-10 | Dissolved | — |
| 21ST CENTURY TRUCKING, INC. | 57821957 | 1994-05-19 | Dissolved | — |
| 21ST CENTURY TRUCKING, INC. | 60561222 | 1999-06-29 | Dissolved | — |
| 21ST CENTURY U.S.-SINO SERVICES, INC. | 61577254 | 2001-03-29 | Active | Chicago |
| 21ST CENTURY UROLOGY, S.C. | 61998578 | 2002-01-14 | Active | — |
| 21ST CENTURY VALUE HOME FURNISHINGS LLC | 05132487 | 2015-01-22 | Dissolved | CHICAGO |
| 21ST CENTURY VENTURES INC. | 68058252 | 2011-08-18 | Dissolved | — |
| 21ST CENTURY VINTAGE DISTRIBUTORS, LLC | 03764079 | 2012-01-26 | Dissolved | CHICAGO |
| 21ST CENTURY VINTAGE LLC | 05799082 | 2016-05-19 | Dissolved | LYNWOOD |
| 21ST CENTURY VISIONARIES | 61491481 | 2001-02-21 | Dissolved | — |
| 21ST CENTURY VOTERS, L.L.C. | 00315435 | 1999-08-13 | Dissolved | BLOOMINGTON |
| 21ST CENTURY WATER INC. | 67388038 | 2010-01-07 | Dissolved | — |
| 21ST CENTURY WEDDING SERVICES, INC. | 66764508 | 2009-11-16 | Dissolved | — |
| 21ST CENTURY WOMAN | 57397381 | 1993-07-20 | Dissolved | — |
| 21ST CENTURY WORKOUT WORLD, INC. | 56965459 | 1992-08-31 | Dissolved | — |
| 21ST CENTURY WORKOUT, INC. | 57059583 | 1992-11-12 | Dissolved | — |
| 21ST CENTURY YOUTH TOWN ORGANIZATION | 53172377 | 1983-08-09 | Dissolved | — |
| 21ST CENTURY, INC. | 55130795 | 1988-06-23 | Dissolved | — |
| 21ST CENTURY, INC. | 59368559 | 1997-04-17 | Dissolved | — |
| 21ST CENTURY, LTD. | 56139664 | 1990-10-15 | Withdrawn | — |
| 21ST CENTURY.COM CONSTRUCTION INC. | 70370824 | 2015-09-28 | Active | — |
| 21ST CENTURY.COM SUSHI INC. | 70370875 | 2015-09-28 | Dissolved | — |