| Cookstown and Western Shores Area Network | Other services | 1998 |
| Cookstown Farms Ltd | Agriculture & fishing | 2016 |
| Cookstown Motor Club Limited | Arts & recreation | 1971 |
| Cool BUS Company Ltd | Transport & logistics | 2019 |
| Coolchain Air Conditioning Ltd | Construction | 2012 |
| Coole Contracts Ltd | Construction | 2021 |
| Coole Retail Ltd | Financial services | 2021 |
| Coolestone Limited | Wholesale & retail | 2014 |
| Coolhill Heavy Haulage Limited | Transport & logistics | 2011 |
| Coolhill Mews Management Company Ltd | Real estate | 2015 |
| Coolmaghery Farms Limited | Agriculture & fishing | 2018 |
| Coolmc Construction Ltd | Construction | 2010 |
| Coolsleeve Ltd | Health & social care | 2018 |
| Cooper Parry Audit (Ireland) Limited | Professional & scientific | 2025 |
| Copytext (NI) Limited | Wholesale & retail | 2003 |
| Copytext Asset Finance Ltd | Financial services | 2016 |
| Copytext Telecom Limited | Information & communication | 2021 |
| Coral Homes Collegeland Limited | Real estate | 2019 |
| Coral Homes Group Limited | Real estate | 2015 |
| Coral Housing Limited | Real estate | 2025 |
| Corick Limited | Real estate | 2000 |
| Corkhill Poultry Holdings Ltd | Real estate | 2026 |
| Corkhill Poultry Ltd | Agriculture & fishing | 2018 |
| Corlea Services Ltd | Construction | 2020 |
| Cornagh Consultancy Ltd | Education | 2019 |
| Cornamaddy Farms Limited | Agriculture & fishing | 2021 |
| Cornamaddy Holdings Limited | Professional & scientific | 2021 |
| Cornamaddy Poultry Ltd | Agriculture & fishing | 2025 |
| Cornamaddy Renewables Limited | Agriculture & fishing | 2014 |
| Corr CF Ltd | Financial services | 2016 |
| Corr DV Ltd | Transport & logistics | 2017 |
| Corra Limited | Construction | 2025 |
| Corrigan Accident Management Ltd | Transport & logistics | 2023 |
| Corrody Events Ltd | Administrative & support | 2021 |
| Corruda Engineering Ltd | Professional & scientific | 2024 |
| Corseer Properties Ltd | Real estate | 2012 |
| Cortex Engineering Solutions Ltd | Professional & scientific | 2021 |
| Cottage Dungannon Ltd | Other services | 2016 |
| Cottage Dungannon Therapies Ltd | Other services | 2019 |
| Cottagequinn Enterprises Ltd | Financial services | 2018 |
| Cottagequinn Farms LLP | | 2018 |
| Country Fuels Limited | Wholesale & retail | 2025 |
| Countryside Services Limited | Manufacturing | 1998 |
| County Coaches Limited | Transport & logistics | 2008 |
| Cove Manor Care Home Limited | Health & social care | 2012 |
| Coventry Drain Unblocking Ltd | Water & waste | 2021 |
| Coxhill Holdings Ltd | Real estate | 2023 |
| CP Audit (Ireland) LLP | | 2025 |
| CP Homes (Ireland) Ltd | Construction | 2016 |
| CPC Office Supplies Limited | Wholesale & retail | 2021 |
| Craigmillar Enterprises Ltd | Professional & scientific | 2025 |
| Craigview Luxury Glamping Ltd | Hospitality | 2023 |
| Cranlome Ltd | Real estate | 2009 |
| Crannogue Eggs Limited | Agriculture & fishing | 2017 |
| Crannogue Engineering Limited | Professional & scientific | 2022 |
| Crannogue Services Limited | Professional & scientific | 2022 |
| Craobh Dhearg Limited | Real estate | 2016 |
| Creative Sweet Ltd | Information & communication | 2026 |
| Creocto Ltd | Professional & scientific | 2019 |
| Creteworx Ltd | Construction | 2020 |
| Crew Carts Ltd | Manufacturing | 2024 |
| Crewe Services Limited | Other services | 2007 |
| Crewroe Management Ltd | Households | 2017 |
| Crievemore Electric Ltd | Construction | 2004 |
| Cristash Limited | Hospitality | 2010 |
| Crock Partnerships Limited | Financial services | 2024 |
| Cronin Agri. Limited | Construction | 2018 |
| Crory Ltd | Construction | 2019 |
| Cross County Fuels Limited | Wholesale & retail | 2017 |
| Cross Veterinary Clinic Ltd | Professional & scientific | 2016 |
| Crosscavanagh Ltd | Real estate | 2025 |
| Crossmeck Limited | Financial services | 2022 |
| Crossrock Limited | Real estate | 2018 |
| CRT T/A Thetoolshed Ltd | Wholesale & retail | 2005 |
| CSC Covert Security Consultants Limited | Administrative & support | 2024 |
| CSL Entertainment Belfast Ltd | Extraterritorial | 2019 |
| Ctqss Ltd | Professional & scientific | 2015 |
| Cuba & Havana Limited | Wholesale & retail | 2014 |
| Cullen Recycling Limited | Water & waste | 2024 |
| Cullenfad Developments Ltd | Real estate | 2026 |
| Culliver Finance Limited | Other services | 2023 |
| Culowen Management Co Limited | Real estate | 2007 |
| Curraghmore House Consultancy Services Ltd | Professional & scientific | 2023 |
| Curran Optometrists Ltd | Health & social care | 2006 |
| Currie Crane Hire Ltd | Administrative & support | 2014 |
| Cushnahan Haulage Ltd | Transport & logistics | 2021 |
| CW 22 Limited | Real estate | 2021 |
| CWS Parts NI Limited | Manufacturing | 2025 |
| Cyril Campbell (Electrics) Limited | Wholesale & retail | 1976 |
| Cyril Campbell (Holdings) Limited | Wholesale & retail | 2015 |
| D & R Construction Limited | Construction | 2002 |
| D and R Moffett Limited | Agriculture & fishing | 2012 |
| D Armstrong Electrical LLP | | 2012 |
| D Blake Electrical Ltd | Construction | 2026 |
| D Campbell Transport Limited | Transport & logistics | 2025 |
| D Gallagher & Sons Ltd | Agriculture & fishing | 2015 |
| D H Corporate Holdings Limited | Financial services | 2016 |
| D&E Hughes Ltd | Manufacturing | 2016 |
| D&M Contracts Limited | Construction | 2020 |
| D&O Poultry Ltd | Agriculture & fishing | 2012 |