| Circet DCS (UK) Limited | Construction | 2017 |
| Cirrus Property Developments Ltd | Real estate | 2015 |
| Cityside Commercial Ltd | Real estate | 2024 |
| Cityside Developments Limited | Construction | 2006 |
| Civil TEC Construction (UK) Limited | Construction | 2025 |
| CJC Market Limited | Wholesale & retail | 2024 |
| CJD Retail Ltd | Wholesale & retail | 2018 |
| CJM Mechanical Services Ltd | Construction | 2022 |
| CK Autotie Balers Ltd | Extraterritorial | 2012 |
| CK International Rentals Ltd | Administrative & support | 2022 |
| CK Legal LLP | | 2023 |
| Clare Hasson Solicitor Limited | Professional & scientific | 2017 |
| Clarity Momentum Group Limited | Professional & scientific | 2025 |
| Classic Marble (Showers) Holding Ltd | Financial services | 2022 |
| Classic Marble (Showers) Limited | Manufacturing | 1993 |
| Clearclaim Ltd | Water & waste | 2023 |
| Clearsky Brewing Company Limited | Manufacturing | 2012 |
| Clearslate Debt Solutions Ltd | Extraterritorial | 2021 |
| Clec Investments Ltd | Construction | 2024 |
| CLG Enviro Ltd | Water & waste | 2025 |
| Climate Source Ltd | Construction | 2014 |
| Cllj Ltd | Hospitality | 2024 |
| Clogher Valley Care Limited | Health & social care | 2007 |
| Clogher Valley Properties Limited | Real estate | 1995 |
| Clogherney Developments Ltd | Construction | 2014 |
| Clogherney Family Holdings Ltd | Real estate | 2023 |
| Clogherney Property Holdings Ltd | Financial services | 2024 |
| Cloghfin Property Investments Ltd | Real estate | 2025 |
| Cloghog Farms Limited | Agriculture & fishing | 2014 |
| Cloghog Properties Ltd | Real estate | 2024 |
| Clonaneese Development Group | Arts & recreation | 2018 |
| Cloncore Farm Limited | Real estate | 2013 |
| Clonmore Packaging Ltd | Wholesale & retail | 2022 |
| Clonmore Regeneration Group Limited | Information & communication | 2012 |
| Clonmore Wholesale LLP | | 2017 |
| Clonty Farms Ltd | Agriculture & fishing | 2010 |
| Clonty Services Ltd | Real estate | 2020 |
| Cloud 9 Wellness & Recovery Ltd | Other services | 2024 |
| Cloughbane Farm Foods Limited | Manufacturing | 2012 |
| Clover Facilities Management Ltd | Construction | 2023 |
| Club Competitions Ltd | Wholesale & retail | 2020 |
| CM Civil Engineering Ltd | Construction | 2015 |
| CM Steel Ltd | Construction | 2023 |
| CM Wheels Limited | Wholesale & retail | 2011 |
| CMC Fibre Ltd | Construction | 2021 |
| CMC Pharmaceutical Consulting Ltd | Professional & scientific | 2020 |
| Cmck Services Ltd | Information & communication | 2021 |
| Cmdd Investments Ltd | Financial services | 2023 |
| CMK Electrical Contractors Ltd | Construction | 2024 |
| CMK Mechanical Services Ltd | Construction | 2011 |
| CML Haulage & Sons Ltd | Transport & logistics | 2017 |
| CMN Holdings Ltd | Professional & scientific | 2021 |
| CMP Roofing & Building Ltd | Construction | 2024 |
| CMV Plant Ltd | Transport & logistics | 2022 |
| Cntury NI Ltd | Wholesale & retail | 2024 |
| Cnug Ltd | Financial services | 2025 |
| Coalisland Community Hub & Foodbank | Administrative & support | 2025 |
| Coalisland Filling Station Ltd | Wholesale & retail | 2016 |
| Coalisland Taxi's Limited | Transport & logistics | 2015 |
| Coar Accident Management Ltd | Transport & logistics | 2025 |
| Cobalt Trade Sale Limited | Wholesale & retail | 2025 |
| COD2 Ltd | Real estate | 2023 |
| Coffee Plus Ltd | Hospitality | 2026 |
| Coffeze Limited | Hospitality | 2010 |
| Cognetic Ltd | Information & communication | 2025 |
| Cohannon Holdings Limited | Wholesale & retail | 2011 |
| COL MC Engineering Ltd | Manufacturing | 2010 |
| Colbon GOC (NI) Limited | Energy | 2009 |
| Coleman Construction Ltd | Construction | 2004 |
| Coleraine Care Centre Ltd | Health & social care | 2014 |
| Colhoun Flooring Ltd | Construction | 2021 |
| Colhoun Properties Ltd | Real estate | 2025 |
| College Square North Property Limited | Real estate | 2015 |
| Collegeland Private Nursing Home Limited | Health & social care | 1990 |
| Colsha Limited | Wholesale & retail | 2022 |
| Comfizone Ltd | Manufacturing | 2005 |
| Community Organisations of South Tyrone and Areas Ltd | Other services | 2002 |
| Compact Screens Ltd | Manufacturing | 2018 |
| Complete Rendering Ltd | Construction | 2019 |
| Conark Ltd | Construction | 2015 |
| Concrete Quarry Info Ltd | Professional & scientific | 2024 |
| Conda Site Services Ltd | Construction | 2017 |
| Confident Kidz Clonoe Ltd | Health & social care | 2024 |
| Confidential Shredding Co (N.I.) Ltd | Administrative & support | 2018 |
| Congo Engineering Ltd | Manufacturing | 2023 |
| Conlect Holdings Ltd | Financial services | 2021 |
| CONNECT2BRILLIANCE CIC | Health & social care | 2024 |
| Connolly & FEE Limited | Construction | 1970 |
| Connolly's Media Ltd | Information & communication | 2017 |
| Connollys of MOY (Outlet Stores) Ltd | Wholesale & retail | 2022 |
| Connollys of MOY Ltd | Wholesale & retail | 2016 |
| Connor Harte Rentals Ltd | Real estate | 2025 |
| Conor & Ellie Ltd | Hospitality | 2015 |
| Conpa Limited | Administrative & support | 2019 |
| Conquer Engineering Limited | Manufacturing | 2020 |
| Construct Group Limited | Professional & scientific | 2026 |
| Construction Fasteners Ireland Limited | Manufacturing | 2006 |
| Container Sales NI 2000 Ltd | Wholesale & retail | 2018 |
| Contract Services DGN Ltd | Water & waste | 2006 |
| Conway Contracts Ltd | Real estate | 2005 |