| Chadwick House (Covent Garden) Flats Management Company Limited | Households | 2021 |
| Chanya Culture Ltd | Arts & recreation | 2023 |
| Chaos Activewear Ltd | Wholesale & retail | 2025 |
| Chapter Two Books Ltd | Wholesale & retail | 2025 |
| Charlannah Ltd | Manufacturing | 2015 |
| Chris Forestry Ltd | Wholesale & retail | 2017 |
| Christian Davies LK Limited | Construction | 2018 |
| CJ Plastering and Rendering Specialists Ltd | Construction | 2024 |
| CLA Property Developments Ltd | Construction | 2025 |
| Cladzone Ltd | Construction | 2024 |
| Clarence House (Llandovery) Management Limited | Professional & scientific | 2008 |
| Classic Jets Ltd | Transport & logistics | 2025 |
| Classo Barber Limited | Other services | 2020 |
| Clear Cloud Technology Ltd | Information & communication | 2025 |
| Cledtry Limited | Construction | 2021 |
| Clives Cabs Tycroes Ltd | Transport & logistics | 2025 |
| CLM Property Holdings Limited | Real estate | 2024 |
| Cloud Genius Ltd | Information & communication | 2011 |
| Clwb Golff Glynhir Golf Club Limited | Arts & recreation | 2022 |
| Clwb Rygbi Betws RFC Limited | Arts & recreation | 2012 |
| Clwb Rygbi Brynaman Limited | Arts & recreation | 2018 |
| Coalfire Cottage Ltd | Energy | 2026 |
| Coaltown Limited | Manufacturing | 2013 |
| Coed TIR George CIC | Hospitality | 2025 |
| Coffee Gear Ltd | Manufacturing | 2011 |
| Colours Hairdressing Limited | Other services | 2004 |
| Complete Accident Solutions Limited | Administrative & support | 2009 |
| Construction Solutions UK (Wales) Ltd | Construction | 2009 |
| Contract UK (Holdings) Limited | Information & communication | 2021 |
| Contract UK LLP | | 2005 |
| Cool Mint Projects Ltd | Construction | 2024 |
| Cool Mint Property Ltd | Households | 2024 |
| Copenhagen Central Limited | Real estate | 2024 |
| Corgi Hosiery Limited | Manufacturing | 1997 |
| Cosmosxr Ltd | Information & communication | 2023 |
| Counterculture Europe Limited | Wholesale & retail | 2024 |
| CP Carpentry Ltd | Manufacturing | 2024 |
| Craig Insurance Services Limited | Financial services | 1998 |
| Crazy Components Ltd | Wholesale & retail | 2024 |
| Crazy Cornocks Limited | Financial services | 2020 |
| CRC Holdings (UK) Limited | Professional & scientific | 2004 |
| Creative Syndicates Tech Ltd | Information & communication | 2026 |
| Crisp N FRY Ammanford Ltd | Hospitality | 2023 |
| Cronfa CYF | Professional & scientific | 2013 |
| Cronfa Mair Ltd | Real estate | 2025 |
| Crossco Associates Limited | Hospitality | 2004 |
| CRT Properties Limited | Real estate | 2018 |
| CS & AS Limited | Wholesale & retail | 2018 |
| CS Property Holdings Limited | Real estate | 2015 |
| CTF Welding Ltd | Professional & scientific | 2026 |
| CTR Enterprises Ltd | Real estate | 2005 |
| Cura Partnerships Ltd | Real estate | 2025 |
| Cwja Properties Limited | Financial services | 2025 |
| Cwmgors RFC Limited | Arts & recreation | 2018 |
| Cwmllwchwr Mill Ltd | Real estate | 2022 |
| Cwmni Ffynnu Productions CIC | Arts & recreation | 2026 |
| Cyfle Building Skills Ltd | Administrative & support | 2013 |
| Cymru Tourist Guide Ltd | Administrative & support | 2005 |
| Cynnal Property Services Limited | Health & social care | 2009 |
| Cyson Management Ltd | Administrative & support | 2024 |
| D Davies Electrical Services Ltd | Construction | 2011 |
| D J Davies Plastering Limited | Construction | 2025 |
| D'Vanguard Property Limited | Real estate | 2024 |
| D. Wynne Evans & Sons Limited | Construction | 2001 |
| DAN Y Lloer CYF. | Agriculture & fishing | 2022 |
| Datod Limited | Professional & scientific | 2001 |
| David Hardwick Fencing Ltd | Construction | 2009 |
| Davies Agri (Wales) Ltd | Agriculture & fishing | 2023 |
| Davies and Sons 1973 Limited | Professional & scientific | 2017 |
| DBL Fire Ltd | Public administration | 2025 |
| DC Business Ventures Limited | Administrative & support | 2020 |
| DCP Accountancy Limited | Professional & scientific | 2019 |
| DCP Office Services Limited | Administrative & support | 2022 |
| Decus Research Limited | Professional & scientific | 2001 |
| DEE JAY Prism Limited | Information & communication | 2016 |
| Deja Services Ltd | Administrative & support | 2013 |
| Dekit Home and Garden Services Limited | Administrative & support | 2017 |
| Delightful Discoveries LLP | | 2025 |
| Delta 1 Castle Ltd | Hospitality | 2024 |
| Demetae Consulting Ltd | Professional & scientific | 2018 |
| Derllys Court Golf Club Limited | Arts & recreation | 2021 |
| Derma-Seal Ltd | Health & social care | 2018 |
| Derwydd Garage Llandybie Limited | Wholesale & retail | 2009 |
| Derwydd Mansion Events Ltd | Hospitality | 2016 |
| Desert Falcons York Limited | Agriculture & fishing | 2023 |
| Devitech Limited | Construction | 2021 |
| DG Auto FIX Ltd Ltd | Wholesale & retail | 2024 |
| DGR Enterprises Limited | Information & communication | 2007 |
| Dinefwr Electrical & Solar Ltd | Construction | 2023 |
| Direct Performance Training Ltd | Professional & scientific | 2019 |
| Divine Health and Beauty Ltd | Other services | 2018 |
| DJ Davies Holdings Ltd | Financial services | 2026 |
| Djec Ltd | Construction | 2019 |
| DL Fire Design Ltd | Professional & scientific | 2026 |
| DO Good Faster LLP | | 2023 |
| Dodion Limited | Information & communication | 2015 |
| Doublescale Limited | Manufacturing | 1982 |
| DR Gina Holmes Ltd | Professional & scientific | 2022 |
| DR Property Developments Ltd | Construction | 2019 |
| DR Weils Limited | Professional & scientific | 2014 |