| CREDERE28 Ltd | Real estate | 2024 |
| Creevagh Consulting Engineers Limited | Professional & scientific | 2022 |
| Creeve Management Ltd | Households | 2017 |
| Cresco Trading Company Limited - the | Transport & logistics | 2004 |
| CRJ Ltd | Health & social care | 2020 |
| CRO Limited | Households | 2025 |
| Croaghross House Ltd | Financial services | 2022 |
| Crockagarran Wind Farm Ltd | Energy | 2007 |
| Cross Concrete Flooring Products Limited | Manufacturing | 2015 |
| Cross County Contracts Ltd | Construction | 2016 |
| Crossan Container Conversions Ltd | Hospitality | 2021 |
| Crossan Jewellers Limited | Wholesale & retail | 2025 |
| Crossan Safety Management Limited | Health & social care | 2024 |
| Crossfit Life CIC | Arts & recreation | 2025 |
| Crosshead Farms Limited | Agriculture & fishing | 2014 |
| Croí Care Ltd | Health & social care | 2025 |
| Cruck Contracts Ltd | Construction | 2024 |
| Crudden Construction Ltd | Construction | 2015 |
| Crumley Developments Ltd | Real estate | 2015 |
| Cráinn Dubh Limited | Professional & scientific | 2026 |
| CSP Mechanical Ltd | Construction | 2026 |
| CT Designsolutions Ltd | Professional & scientific | 2023 |
| CT Shopfitting Limited | Construction | 2022 |
| Cubicon Games Limited | Information & communication | 2025 |
| Cuil Darach Limited | Hospitality | 2016 |
| Cula Convenience Ltd | Wholesale & retail | 2024 |
| Culcirrus Ltd | Information & communication | 2024 |
| Culmore Creams Ltd | Wholesale & retail | 2025 |
| Culmore Properties Ltd | Real estate | 2004 |
| Culmore View Properties Ltd | Real estate | 2018 |
| Cultural Smart HR Ltd | Information & communication | 2025 |
| Cultural Staffing Solutions Ltd | Professional & scientific | 2024 |
| Culture Education Exchange Consulting Limited | Education | 2016 |
| Cunamh | Health & social care | 2000 |
| Cuppa Joe's Coffee 2 Go Ltd | Wholesale & retail | 2025 |
| Curley Cars Ltd | Wholesale & retail | 2018 |
| Curry's Amusements Ltd | Arts & recreation | 2014 |
| Curryfree Wind Farm Limited | Energy | 2008 |
| Currynierinstores Limited | Wholesale & retail | 2024 |
| Currys Fresh Food Limited | Wholesale & retail | 2023 |
| Currys Garage Limited | Wholesale & retail | 2014 |
| Curzon Projects Ltd | Real estate | 2015 |
| Custom Parlour Ltd | Other services | 2025 |
| Cute Properties Limited | Households | 2023 |
| Cutting Edge Helicopters Ltd | Transport & logistics | 2012 |
| CVA Properties Limited | Real estate | 2025 |
| CW Linecraft Ltd | Construction | 2025 |
| CXO Solutions Ltd | Professional & scientific | 2026 |
| CYB Independent Social Work Consultancy Ltd | Health & social care | 2020 |
| Cyber Knox Solutions Ltd | Information & communication | 2025 |
| Céad Music Ltd | Arts & recreation | 2019 |
| D & a Brickworks Limited | Construction | 2018 |
| D & M Farm Services Limited | Wholesale & retail | 2006 |
| D & N Tyres Ltd | Wholesale & retail | 2023 |
| D - Seven Projects Limited | Real estate | 1998 |
| D a Miller & Sons (Transport) Limited | Transport & logistics | 2010 |
| D Barr Joinery Ltd | Construction | 2015 |
| D Breslin Joinery Ltd | Construction | 2018 |
| D Butler Healthcare Ltd | Wholesale & retail | 2020 |
| D Davis Plant Limited | Construction | 2026 |
| D Forklifts Limited | Wholesale & retail | 2019 |
| D J Developments Ireland Limited | Real estate | 2025 |
| D K Remediation Ltd | Water & waste | 2011 |
| D M D Car Sales Ltd | Wholesale & retail | 2023 |
| D Russell Holdings Ltd | Financial services | 2025 |
| D&D Auto Services Limited | Wholesale & retail | 2021 |
| D&T Competitions Ltd | Other services | 2025 |
| D-Flow Designs Ltd | Manufacturing | 2021 |
| D-Mac Joinery Limited | Construction | 2014 |
| D. R. Downey Ltd | Other services | 2018 |
| D.C. Black Holding Limited | Financial services | 2007 |
| D.G. Cleaning Services Limited | Administrative & support | 2019 |
| D.W.N. Developments Limited | | 2002 |
| D.Z Commissioning Services Limited | Construction | 2025 |
| D4 Property Ltd | Real estate | 2022 |
| D4 Solutions Ltd | Information & communication | 2021 |
| Dack Couriers Ltd | Transport & logistics | 2021 |
| Dacre Services Limited | Hospitality | 2023 |
| Daly Autos Ltd | Wholesale & retail | 2020 |
| Damian Millar Building Ltd | Manufacturing | 2015 |
| Damien Mccauley Trading Limited | Wholesale & retail | 2016 |
| Dams Contractors Ltd | Construction | 2024 |
| Daniel Sarhan Ltd | Health & social care | 2023 |
| Danny MAC Utilities Ltd | Construction | 2026 |
| Danny O’Neills Ltd | Hospitality | 2019 |
| Danu Trading Limited | Wholesale & retail | 2025 |
| Dapper Clothes Limited | Wholesale & retail | 2021 |
| Dara Catering Ltd | Hospitality | 2025 |
| Darcon G Limited | Transport & logistics | 2026 |
| Darin Lace Ltd | Hospitality | 2003 |
| Dart Mountain Cheese Ltd. | Manufacturing | 2015 |
| Datacabs (Derry) Limited | Transport & logistics | 2011 |
| Davenham Switchgear UK & Northern Ireland Limited | Manufacturing | 2021 |
| David a Watt & Co (Investments) Ltd | Real estate | 2022 |
| David a Watt & Co (Sales Co) Limited | Extraterritorial | 2019 |
| David Kinnear Transport Limited | Transport & logistics | 2014 |
| Dawn Safety & Compliance Limited | Professional & scientific | 2025 |
| Day Tours London Ltd | Transport & logistics | 2014 |
| Dazone Properties Ltd | Real estate | 2025 |
| DBL Consultancy Services Limited | Administrative & support | 2024 |