| Cleaton’S Sports Champs Ltd | Education | 2025 |
| Cledwyn Saunders & SON Limited | Manufacturing | 1977 |
| CLM Windows & Doors Limited | Construction | 2020 |
| Co Infrastructure Services Ltd | Information & communication | 2026 |
| Coal and Cables Ltd | Information & communication | 2026 |
| Coco's Coffee Limited | Hospitality | 2024 |
| Coedcae Farm Energy Limited | Energy | 2025 |
| Coedcae Farm Limited | Agriculture & fishing | 2020 |
| Coffee Blue Aberdare Ltd | Wholesale & retail | 2019 |
| Comfy Products Limited | Manufacturing | 2022 |
| Commando Fit Aberdare Ltd | Health & social care | 2021 |
| Commando Fit Dare Valley CIC | Education | 2023 |
| Commercial Utility Brokers.Com Limited | Wholesale & retail | 2009 |
| Commercial Vehicle Consultancy Ltd | Professional & scientific | 2026 |
| Complete Estates Maintenance Ltd | Construction | 2019 |
| Connect MG2 Ltd | Wholesale & retail | 2023 |
| Connolly Integrated Services Ltd | Agriculture & fishing | 2025 |
| Conroy Promotions Ltd | Administrative & support | 2024 |
| Construction Safety Services Limited | Financial services | 2025 |
| Cooking Space Ltd | Wholesale & retail | 2019 |
| Cornsy Services Limited | Construction | 2004 |
| Crafted by Rose Ltd | Other services | 2018 |
| CRD Property & Development Ltd | Real estate | 2026 |
| Crown Race Media Ltd | Information & communication | 2024 |
| Crux CDM Ltd | Professional & scientific | 2020 |
| CS Renovations Carpentry + Plastering Ltd | Manufacturing | 2026 |
| Ctd-Training & Consultancy Ltd | Professional & scientific | 2012 |
| Cub-Wales Ltd | Wholesale & retail | 2009 |
| Currentmax Innovations Ltd | Construction | 2025 |
| Curtis and Gibson Ltd | Manufacturing | 2009 |
| CVA Building Limited | Construction | 2007 |
| CWM Agricultural Limited | Administrative & support | 2007 |
| Cwmaman Arts Centre | Arts & recreation | 2018 |
| Cwmaman Gym Ltd | Arts & recreation | 2019 |
| Cwmaman Retail Store Limited | Wholesale & retail | 2026 |
| Cwmdare Miners' Welfare Social Club Limited | Hospitality | 2006 |
| Cwmdare Traders Limited | Wholesale & retail | 2013 |
| Cwtch Kitchen Aberdare Ltd | Hospitality | 2026 |
| Cygnus Developments Limited | Construction | 2013 |
| Cylch Meithrin Penderyn C.I.C. | Administrative & support | 2018 |
| Cymoedd Creadigol CIC | Education | 2020 |
| Cynon Contract Services Ltd | Construction | 2023 |
| Cynon Rentals Ltd | Real estate | 2026 |
| Cynon Valley Organic Adventures Ltd | Agriculture & fishing | 2018 |
| D & R Tiles Ltd | Wholesale & retail | 2003 |
| D & S Phillips Property Ltd | Real estate | 2023 |
| D D Design and Consultancy Ltd | Professional & scientific | 2023 |
| D Electrical Ltd | Construction | 2025 |
| D Evans Plant Ltd | Administrative & support | 2022 |
| D Evans Plant Training Ltd | Education | 2022 |
| D Evans QS Consultancy Ltd | Professional & scientific | 2025 |
| D J Blad Ltd | Professional & scientific | 2025 |
| D J Davies Haulage (South Wales) Limited | Transport & logistics | 2005 |
| D J Harrison Ltd | Professional & scientific | 2009 |
| D M Caviell Services Limited | Construction | 2018 |
| D Meredith Plant & Agri Services Limited | Agriculture & fishing | 2026 |
| D&A Carpentry Specialist Limited | Construction | 2003 |
| D&A Connections Limited | Construction | 2018 |
| D&S Roofing and Cladding Limited | Administrative & support | 2024 |
| D.P. Air Conditioning & Refrigeration Ltd | Construction | 2026 |
| Dafloc Digital Consults Limited | Information & communication | 2025 |
| DAI the Handyman Ltd | Construction | 2019 |
| Daisy Fresh Home Fragrances Ltd | Wholesale & retail | 2024 |
| Dan's Telecom Solutions Limited | Information & communication | 2017 |
| Dare Building Services Ltd | Construction | 2025 |
| Dare Fitness Ltd | Education | 2017 |
| Dare Valley Chiropractic Limited | Health & social care | 2009 |
| Dare Valley Trout Fishery Ltd | Agriculture & fishing | 2020 |
| Darfin Properties Ltd | Real estate | 2017 |
| Dass Property Solutions Limited | Real estate | 2018 |
| Dave"S Family Butchers Limited | Wholesale & retail | 2013 |
| David Leigh Productions Limited | Arts & recreation | 2025 |
| Davies Brothers (Wales) Limited | Construction | 1994 |
| Davies Companies Limited | Financial services | 2024 |
| Dawell Ltd | Construction | 2023 |
| DAZ Plant and Labour Ltd | Administrative & support | 2022 |
| DCA Construction Ltd | Construction | 2026 |
| DCL Associates Limited | Real estate | 2003 |
| DCN Property Developments Ltd | Real estate | 2023 |
| Dean Owens Services Limited | Administrative & support | 2022 |
| DEC Global Group Ltd | Financial services | 2025 |
| Dec-Elec Ltd | Construction | 2020 |
| Dec-Renewables Ltd | Construction | 2025 |
| DEE Light Services Ltd | Real estate | 2024 |
| Deesale Ltd | Wholesale & retail | 2026 |
| Deka Property Co Ltd | Hospitality | 2023 |
| Demer Property Ltd | Real estate | 2022 |
| Dendrocopos Limited | Information & communication | 2010 |
| Derw Property Ltd | Real estate | 2024 |
| DGD Civils Ltd | Construction | 2022 |
| DGE Holdings Ltd | Financial services | 2023 |
| Diane Stark Health Limited | Health & social care | 2019 |
| Digital Nomads for Good C.I.C. | Financial services | 2023 |
| Dignified Pet Cremations Ltd | Other services | 2024 |
| Dillons Demolition Ltd | Water & waste | 2025 |
| Dinomania Ltd | Arts & recreation | 2015 |
| Diverse Training Solutions Ltd | Education | 2025 |
| Djmcivils Ltd | Construction | 2022 |
| DJP Fabrication Ltd | Manufacturing | 2019 |
| DK Drylining Ltd | Construction | 2024 |