| CCC Technical Limited | Professional & scientific | 2023 |
| CCS Consultancy Ltd | Professional & scientific | 2019 |
| CDK Group Ltd | Construction | 2018 |
| CEA Rentals Ltd | Real estate | 2020 |
| CEA Vision Ltd | Health & social care | 2015 |
| Ceapach Properties Ltd | Real estate | 2025 |
| Celine's Fashions Ltd | Wholesale & retail | 2012 |
| Celtonn Technology Limited | Professional & scientific | 2024 |
| Centenary Enterprise Ltd | Professional & scientific | 2025 |
| CFM Contracts Ltd | Construction | 2022 |
| CFP Properties Ltd | Real estate | 2023 |
| CFS (Ireland) Limited | Construction | 2015 |
| CFS (Ireland) Plant Limited | Administrative & support | 2025 |
| CG Poultry Ltd | Agriculture & fishing | 2025 |
| Chalk Fitness Ltd | Arts & recreation | 2020 |
| Chaz Developments Ltd | Construction | 2022 |
| Chequered Flag Competitions Ltd | Arts & recreation | 2026 |
| Chesterfield Holdings Limited | Health & social care | 2020 |
| Chieftan Construction Ltd | Professional & scientific | 2026 |
| CHL Plant Hire Ltd | Administrative & support | 2015 |
| Chopsticks Newtownstewart Ltd | Hospitality | 2023 |
| CHP Services (N.I.) Ltd | Manufacturing | 2019 |
| Chung HIM Ltd | Real estate | 2012 |
| Cinq Properties Ltd | Real estate | 2003 |
| Circuits Complete Limited | Construction | 2009 |
| Circular Property Developments Ltd | Construction | 2013 |
| City Bar and Kitchen Ltd | Hospitality | 2021 |
| Civil Engineering Ireland Limited | Construction | 2012 |
| Civil Utilities Construction Ltd | Construction | 2026 |
| Civils Material Testing Limited | Manufacturing | 2018 |
| Civils R US Limited | Construction | 2018 |
| Cjep Limited | Agriculture & fishing | 2018 |
| CJM Group Ltd | Wholesale & retail | 2024 |
| CJX Investments Ltd | Administrative & support | 2021 |
| Ckpmg Limited | Real estate | 2015 |
| Claggan Properties Ltd | Real estate | 2026 |
| Clanabogan Developments Limited | Construction | 2014 |
| Clanabogan Properties Limited | Real estate | 2000 |
| Clanaboggan Property Management Limited | Households | 2006 |
| Clar Renewable Energy Limited | Construction | 2015 |
| Claragh Energy Ltd | Energy | 2020 |
| Claragh Homes Ltd | Construction | 2015 |
| Claraghlea Ltd | Professional & scientific | 2020 |
| Claraghlea Professional Services Ltd | Construction | 2024 |
| Claramore Limited | Construction | 2014 |
| Claremore Energy Ltd | Energy | 2022 |
| Claremount (Omagh) Limited | Professional & scientific | 2014 |
| Clarity Scanning & Holistic Health Ltd | Health & social care | 2023 |
| Clarke Road Contracts Limited | Construction | 2006 |
| Classic Service Station Limited | Wholesale & retail | 2005 |
| Clavon Investments Limited | Real estate | 1994 |
| Cleanbee Services Ltd | Administrative & support | 2023 |
| Cleanforceni Ltd | Administrative & support | 2021 |
| Cleantec Equipment Ltd | Other services | 2014 |
| Clearstone by Heart Ltd | Wholesale & retail | 2025 |
| Cljm Wholesale Ltd | Wholesale & retail | 2024 |
| Clogher Valley Materials Limited | Mining & quarrying | 2024 |
| Clogher Valley Precision Ltd | Manufacturing | 2004 |
| Clogher Valley Windows Limited | Construction | 2012 |
| Clonavon Limited | Real estate | 2024 |
| Clonleaf Limited | Financial services | 2017 |
| Clonmore Contracts Ltd | Construction | 2015 |
| Cloud Application Services Ltd | Information & communication | 2021 |
| Club Energy (Omagh) Ltd | Arts & recreation | 2013 |
| CM Concrete Flooring Ltd | Construction | 2020 |
| CM Construction (Ireland) Ltd | Construction | 2017 |
| Cmac Contracts Limited | Construction | 2013 |
| Cmac Groundworks Ltd | Agriculture & fishing | 2022 |
| CMB Cabling Contractors Ltd | Construction | 2025 |
| CMB Concrete Flooring Ltd | Construction | 2026 |
| CMC Mobile Plant Services Ltd | Administrative & support | 2010 |
| CMC Plant & Commercials Ltd | Wholesale & retail | 2017 |
| CMC Property Management Ltd | Real estate | 2024 |
| Cmcg Legal (NI) Limited | Professional & scientific | 2020 |
| CMD Power Control Ltd | Construction | 2018 |
| Cmds Property Ltd | Construction | 2022 |
| CMK Contracts Ltd | Construction | 2020 |
| CML Construction Ltd | Construction | 2016 |
| CMP 3 Limited | Professional & scientific | 2024 |
| Coastal Properties Limited | Real estate | 1995 |
| Coffee at Grinders Ltd | Hospitality | 2016 |
| Coincidence Pictures Ltd | Information & communication | 2021 |
| Collins Contracts Ltd | Construction | 2011 |
| Colton Agri Sales Ltd | Wholesale & retail | 2017 |
| Colton Concrete Limited | Manufacturing | 2005 |
| Colton Plant Hire Ltd | Transport & logistics | 2018 |
| Combra Properties Limited | Real estate | 2003 |
| Comech Engineering Ltd | Manufacturing | 2016 |
| Commercial Plant Ireland Ltd | Administrative & support | 2025 |
| Commercial Talent Solutions Ltd | Administrative & support | 2023 |
| Complete Audio Visual Solutions Ltd | Professional & scientific | 2022 |
| Complete Beverage Services Limited | Transport & logistics | 1996 |
| Complete Stainless Solutions (N.I.) Ltd | Construction | 2021 |
| Composite Design Ireland LLP | | 2006 |
| Composite Design Ltd | Construction | 2003 |
| Concrete Plus Ltd | Construction | 2020 |
| Conflooring Ltd | Construction | 2026 |
| Conmor Contracts Ltd | Construction | 2022 |
| Connate Connection Ltd | Other services | 2026 |
| Connex Telecoms Ltd | Information & communication | 2025 |