| CMQ Consulting Limited | Professional & scientific | 2019 |
| Coast Road Management Company Limited | Hospitality | 2008 |
| Cobp Ltd | Professional & scientific | 2025 |
| Cobry Properties Limited | Administrative & support | 2017 |
| COG Contracts Limited | Construction | 2013 |
| Cois Coille Services Limited | Administrative & support | 2010 |
| Colemac Specialist Contracts Limited | Construction | 2012 |
| Colin J R Scott Ltd | Administrative & support | 2012 |
| Colington Limited | Administrative & support | 1989 |
| College Farm Hydro Limited | Energy | 2015 |
| Comfort Needs Limited | Other services | 2017 |
| Commercial Appliance Limited | Manufacturing | 2018 |
| Commercial Connect Limited | Financial services | 2023 |
| Commercial Parts Hub Limited | Wholesale & retail | 2024 |
| Commercial Plant Spraying Limited | Construction | 2025 |
| Community Focus Learning | Information & communication | 2001 |
| Compassion Group Network | Other services | 2015 |
| Compassion Ministries | Other services | 2010 |
| Complifm Limited | Administrative & support | 2024 |
| Con-Lan Logic Ltd | Professional & scientific | 2026 |
| Connect Ministries | Professional & scientific | 1997 |
| Connect Tech AV Limited | Information & communication | 2024 |
| Connolly's Bar and OFF Sales | Wholesale & retail | 2009 |
| Connon Associates Limited | Professional & scientific | 2005 |
| Conor Agnew & Co. Property Limited | Real estate | 2020 |
| Consarfin Investments Limited | Hospitality | 2026 |
| Consciousness Gradient Theory Group Ltd | Information & communication | 2025 |
| Constantin Blotu Ltd | Health & social care | 2024 |
| Contract Engineers Ltd | Construction | 2013 |
| Coolgreaney Investments Limited | Construction | 1995 |
| Coolmar Kells Ltd | Wholesale & retail | 2016 |
| Coolmar Ltd | Wholesale & retail | 2010 |
| Copious Global Trading Ltd | Education | 2019 |
| Copper Contracts Ltd | Construction | 2019 |
| Copywork Ltd | Hospitality | 2011 |
| Corbett Joinery Services Limited | Construction | 2025 |
| Corbo Holdings Limited | Real estate | 2021 |
| Corbo Limited | Real estate | 1995 |
| Corcra Services Ltd | Education | 2019 |
| Coreline Limited | Manufacturing | 2016 |
| Corin Berry Associates Limited | Financial services | 2006 |
| Cornerstone Group Limited - the | Professional & scientific | 1999 |
| Cornmill Manor Management Company Ltd | Households | 2023 |
| Corporate Coaching Solutions Limited | Transport & logistics | 2020 |
| Coshkib Holdings Ltd | Wholesale & retail | 2019 |
| Cosmetic Beautyworks Ltd | Wholesale & retail | 2017 |
| Cosmetic Laserworks Ltd | Other services | 2016 |
| Cosydent Ltd | Health & social care | 2023 |
| Coulter Wealth Associates Ltd | Financial services | 2026 |
| Cova Properties Limited | Construction | 2005 |
| CP Kennedy Transport Ltd | Transport & logistics | 2018 |
| CPC Contracts (N.I.) Ltd | Construction | 2015 |
| CPK Assets | Real estate | 2025 |
| CPS Damptex Ltd | Construction | 2021 |
| CPS Remcon Ltd | Construction | 2026 |
| CPS Remedial (NI) Ltd | Construction | 2015 |
| Craig Court Services Limited | Administrative & support | 1982 |
| Craig Hall | Financial services | 2017 |
| Craigdoo Power Limited | Energy | 2015 |
| Craigfad Farm Holsteins Limited | Agriculture & fishing | 2021 |
| Craigfad Farm Limited | Agriculture & fishing | 2015 |
| Craigfad Poultry Ltd | Agriculture & fishing | 2018 |
| Craignamaddy Distillery Ltd | Manufacturing | 2024 |
| Craigstown Livestock Limited | Agriculture & fishing | 2023 |
| Craig’S Consulting N.I Ltd | Professional & scientific | 2025 |
| Cranmore Leisure Holdings Ltd | Financial services | 2025 |
| Crann Dara Limited | Information & communication | 2017 |
| Cranny Hydro Co Ltd | Energy | 2014 |
| Cranswick Country Foods (Ballymena) | Manufacturing | 2008 |
| Crawford Auctions Ltd | Extraterritorial | 2010 |
| Crawford Close Management Limited | Real estate | 2013 |
| Crawford's Catering Limited | Extraterritorial | 2020 |
| Crawhill Properties Limited | Administrative & support | 2016 |
| Creggan Brick Cutting Ltd | Construction | 2023 |
| Cresk Ltd | Real estate | 2019 |
| Crosshill Holdings Ltd | Financial services | 2020 |
| Crown & Glory Ltd | Other services | 2025 |
| Crystal Tide Ltd | Agriculture & fishing | 2017 |
| CSP and Maintenance Ltd | Construction | 2026 |
| CT Mentors Limited | Health & social care | 2020 |
| Cupbox Ltd | Manufacturing | 2019 |
| Curious Little Things Ltd | Manufacturing | 2025 |
| Curragh Hill Management Limited | Extraterritorial | 2007 |
| Curragh Van Sales Limited | Wholesale & retail | 2022 |
| Cushendun Building Preservation Trust | Arts & recreation | 2007 |
| Custom Reuse Recycle Ltd | Manufacturing | 2024 |
| CUT Bros Ltd | Wholesale & retail | 2024 |
| Cyberforce Security Ltd | Information & communication | 2025 |
| D & M Fixing and Joinery Ltd | Construction | 2020 |
| D B Building Contracts Ltd | Construction | 2003 |
| D G & R Services Limited | Construction | 2026 |
| D J R Plumbing & Heating Services Limited | Construction | 2021 |
| D Kennedy & Co (Ballymena) Ltd | Health & social care | 2021 |
| D Kennedy & Co (Belfast) Ltd | Health & social care | 2021 |
| D Kennedy & Co (Magherafelt) Ltd | Health & social care | 2021 |
| D Kennedy & Co (UK) Ltd. | Health & social care | 2013 |
| D Kennedy Holdings Ltd | Financial services | 2021 |
| D Leslie Holdings Limited | Professional & scientific | 2018 |
| D Leslie Properties Limited | Construction | 2020 |
| D M M I Construction Ltd | Construction | 2005 |