| Christian AID Ireland | Administrative & support | 2006 |
| Christian Fellowship Church | Other services | 2013 |
| Christian Unions Ireland (NI) Trust | Other services | 1998 |
| Christie Properties Ltd | Real estate | 2015 |
| Christine Grove Apartments Limited | Extraterritorial | 1988 |
| Christine Mews Ltd | Households | 2013 |
| Christopher Cooley Contracts Ltd | Construction | 2013 |
| Christopher Highgarden Limited | Wholesale & retail | 2025 |
| Christopher Moss Ltd | Professional & scientific | 2020 |
| Chroma Lighting (N.I.) Ltd | Administrative & support | 1998 |
| Chromadex UK Limited | Extraterritorial | 2014 |
| Chsd Properties Ltd | Real estate | 2024 |
| CHU Chen Limited | Wholesale & retail | 2025 |
| Chub Secure Storage Ltd | Transport & logistics | 2020 |
| Chubby Cherub Coffee Co. Ltd | Hospitality | 2014 |
| Chubby Cherub Holdings Limited | Financial services | 2021 |
| Chubby Cherub Lisburn Road Limited | Hospitality | 2021 |
| Chun Aawi Ltd | Wholesale & retail | 2024 |
| Chunky Games Ltd | Information & communication | 2025 |
| Chunxiu Limited | Wholesale & retail | 2025 |
| Church Court (Holywood) Management Company Limited | Extraterritorial | 2004 |
| Church Hill Wind Farm Limited | Energy | 2004 |
| Church Lane Deli Ltd | Hospitality | 2015 |
| Church Mews Management Company (Newtownabbey) Limited | Households | 2019 |
| Church Mission Society of Northern Ireland | Education | 2025 |
| Church of Ireland and Methodist Chaplaincy Belfast | Other services | 2021 |
| Church of Ireland Orphans and Childrens Society for the Counties of Antrim and Down | Other services | 2003 |
| Church of Ireland Trustees. | Other services | 1924 |
| Church Quarter Management Company Limited | Real estate | 2014 |
| Church Road Developments (Newtownbreda) Ltd | Construction | 2020 |
| Church Road NO.17 Management Limited | Real estate | 2003 |
| Church Street Warrenpoint Management Limited | Households | 2025 |
| Church Valley Homes Limited | Real estate | 2013 |
| Church View (Ballygawley) Management Company Limited | Households | 2019 |
| Churchgate Property Management Co Ltd | Households | 2003 |
| Churchill Mouldings Limited | Administrative & support | 2004 |
| Churchills Cleaners Limited | Real estate | 1995 |
| Churchside Manor Management Company Ltd | Extraterritorial | 2006 |
| Churchview Cottages Management Company Limited | Households | 1999 |
| Chxuelei Limited | Wholesale & retail | 2023 |
| Chysoma Limited | Other services | 2025 |
| CI Trust | Health & social care | 2020 |
| Cialeen Holdings Limited | Real estate | 2022 |
| Ciall Group Ltd | Professional & scientific | 2025 |
| Cian M Dynes Ltd | Construction | 2025 |
| Cian Moran Property Ltd | Real estate | 2025 |
| Ciaran Sheehan Holdings Unlimited | Financial services | 2022 |
| Ciaran Stow Limited | Arts & recreation | 2019 |
| Ciasopert Ltd | Wholesale & retail | 2025 |
| CIC Films Ltd | Information & communication | 2017 |
| CIC Ireland Limited | Information & communication | 2024 |
| CIF III LP | | 2024 |
| Ciggy Vapes Dromore Ltd | Wholesale & retail | 2019 |
| CIL Management Ltd | Financial services | 2023 |
| Cilni Enterprises CIC | Administrative & support | 2024 |
| Cimaomega - Unlock Potential Ltd | Professional & scientific | 2021 |
| Cimpina Limited | Manufacturing | 1990 |
| Cincinational Ltd | Wholesale & retail | 2025 |
| Cine Media Limited | Information & communication | 2005 |
| Cinelingo Ltd | Information & communication | 2023 |
| Cinemagic Limited | Administrative & support | 1998 |
| Cinemagic Productions Limited | Administrative & support | 2013 |
| Cinemagic Productions NO.1 Limited | Administrative & support | 2016 |
| Cinemagicmusic Limited | Administrative & support | 2005 |
| Cinepark Limited | Information & communication | 2026 |
| Cinna 1 Ltd | Hospitality | 2020 |
| Cioe&It Northern Ireland Ltd | Education | 2025 |
| Cipago Estates Limited | Real estate | 2005 |
| Cipchurch Acquisitions Limited | Financial services | 2025 |
| Cipchurch Holdings Limited | Financial services | 2025 |
| Cipchurch MIP Limited | Financial services | 2025 |
| Circadian Capital Limited | Financial services | 2011 |
| Circle Agile Limited | Wholesale & retail | 2023 |
| Circle K Energy Limited | Wholesale & retail | 1978 |
| Circuitstream Ltd | Information & communication | 2024 |
| Circular Data Solutions Holdings Limited | Financial services | 2022 |
| Circular Data Solutions Limited | Manufacturing | 2015 |
| Circular Developments One Ltd | Construction | 2018 |
| Circular Tech Solutions Limited | Wholesale & retail | 2022 |
| Cistunos Ltd | Wholesale & retail | 2025 |
| Citity Limited | Wholesale & retail | 2024 |
| Citizen Sea | Professional & scientific | 2019 |
| Citron Singer Limited | Financial services | 1972 |
| Citrus Properties Limited | Administrative & support | 2014 |
| City Auction (Peterborough) Limited | Wholesale & retail | 2017 |
| City Auction Omagh Limited | Wholesale & retail | 2020 |
| City by Nights Architects Ltd | Professional & scientific | 2024 |
| City Car Sales Ltd | Wholesale & retail | 2025 |
| City Contract Cleaners Limited | Administrative & support | 1991 |
| City Court Property Limited | Real estate | 2010 |
| City Escapes PVT Limited | Real estate | 2025 |
| City Facilities Management (Northern Ireland) Limited | Administrative & support | 2007 |
| City Flooring Centre Ltd | Wholesale & retail | 2010 |
| City Gate Property Management Company Limited | Real estate | 1999 |
| City Industrial Waste Limited | Water & waste | 2003 |
| City Park Property Limited | Real estate | 2017 |
| City Property Management Ltd | Households | 2024 |
| City Quays Car Park Limited | Hospitality | 2017 |
| City Quays Hotel Limited | Hospitality | 2017 |
| City Self TAN Ltd | Other services | 2026 |