| Copson Properties Ltd | Real estate | 2025 |
| Cordera Limited | Professional & scientific | 2015 |
| CORE4 Utilities Ltd | Information & communication | 2026 |
| Cornforth Industrial Services Limited | Construction | 2003 |
| Cornforth Secure Storage Ltd | Transport & logistics | 2020 |
| Corrus RCF Limited | Construction | 2017 |
| Cosmetic Safety Solutions Ltd | Professional & scientific | 2022 |
| Cosygreen Ltd | Real estate | 2023 |
| Coulcon Limited | Professional & scientific | 2013 |
| Coundon and Leeholme Early Years Centre C.I.C. | Education | 2006 |
| Coundon and Leeholme Neighbourhood Area C.I.C. | Professional & scientific | 2025 |
| Coundon Cuts (NE) Ltd | Other services | 2025 |
| Countrywide Protection Ltd | Financial services | 2019 |
| County Durham Legal Services Limited | Professional & scientific | 2011 |
| County Durham Taxis Limited | Transport & logistics | 2024 |
| County Services (Plumbing and Heating) Limited | Construction | 2005 |
| Cowmoonicate Limited | Information & communication | 2018 |
| Craft House Bars (BA) Ltd | Hospitality | 2022 |
| Craggwood Leisure Limited | Hospitality | 2001 |
| Craig Hobson Construction Limited | Construction | 2015 |
| Crakehall Management Company Limited | Real estate | 2017 |
| Crawleas Farming Limited | Agriculture & fishing | 2008 |
| CRE8IVE Graphics Limited | Manufacturing | 2004 |
| Creator Cards Ltd | Information & communication | 2024 |
| Cristy James Ltd | Wholesale & retail | 2022 |
| Crosby Weighing Limited | Manufacturing | 2011 |
| Crossfit ALL OUT Limited | Arts & recreation | 2014 |
| CRS Climate Solutions Ltd | Professional & scientific | 2021 |
| CT Fencing & Landscaping Ltd | Construction | 2023 |
| Cullen & Davies Limited | Construction | 2006 |
| Cultural Enterprises (Trading) Limited | Other services | 2013 |
| Cunningham Property and Investments Ltd | Real estate | 2020 |
| Cura Healthcare Limited | Wholesale & retail | 2021 |
| Curious Matter Productions Ltd | Information & communication | 2024 |
| Curious Therapeutics Limited | Information & communication | 2026 |
| CURIOUS12 Limited | Professional & scientific | 2013 |
| Custom Craft Glass UK Ltd | Wholesale & retail | 2019 |
| CVC Contractors Ltd | Water & waste | 2025 |
| CWE (N.E.) Limited | Construction | 2007 |
| D J Rowland Rentals Limited | Administrative & support | 2016 |
| D Knox Consultancy Limited | Professional & scientific | 2018 |
| D N Malkin Farriery Services Ltd | Administrative & support | 2020 |
| D on Aesthetics and Training Limited | Other services | 2024 |
| D Stewart Scaffolding Ltd | Construction | 2001 |
| D T T Groundworks Ltd | Administrative & support | 2019 |
| D Young Plumbing and Heating Ltd | Construction | 2023 |
| D.A.F. Timber Limited | Manufacturing | 1987 |
| D.R. Palmer & Associates Limited | Professional & scientific | 1995 |
| D.W. Forestry Limited | Agriculture & fishing | 2011 |
| D.W. Walton Stonemason and Builders Limited | Construction | 2004 |
| D3 UK Holdings Ltd | Real estate | 2017 |
| D3-UK Limited | Professional & scientific | 1998 |
| Dabble Duck Properties Limited | Real estate | 2016 |
| Dainvest Ltd | Extraterritorial | 2020 |
| Daisy Arts (NE) CIC | Arts & recreation | 2020 |
| Dale & Wears Property Management Limited | Professional & scientific | 2024 |
| Dale's Mobile Shop Limited | Wholesale & retail | 2016 |
| Dalesview Harrogate Management Company Limited | Households | 2024 |
| Daniel Wilkinson Limited | Extraterritorial | 2016 |
| Daniel's Refrigerated Transport Limited | Transport & logistics | 1997 |
| Danny Wood Builders Limited | Construction | 2011 |
| Dante's Fish Enterprises Ltd | Wholesale & retail | 2024 |
| Dapple IT Services Ltd | Agriculture & fishing | 2021 |
| Dare Logic Ltd | Information & communication | 2024 |
| Darlington Boxing & Martial Arts Academy Limited | Health & social care | 2014 |
| Darryl Meadows Roofing & Cladding Ltd | Construction | 2016 |
| Datalynes Consulting Limited | Information & communication | 2011 |
| Davey Grant MMA Ltd | Arts & recreation | 2019 |
| David Clough Consultants Limited | Professional & scientific | 2025 |
| David Steel Glazing & Joinery Ltd | Construction | 2016 |
| David T Scott & Co Limited | Professional & scientific | 2012 |
| David T Scott Accountants Limited | Professional & scientific | 2023 |
| Davidsons of Coundon (Bulk Haulage) Limited | Information & communication | 1977 |
| Davies Technical Consultancy Limited | Professional & scientific | 2026 |
| Day Care of Dogs Limited | Other services | 2022 |
| Day Gill Farm Boarding Ltd | Agriculture & fishing | 2025 |
| Dayal Holdings Ltd | Real estate | 2017 |
| Dayal Real Estate Limited | Real estate | 2017 |
| DB Groundworks (NE) Ltd | Construction | 2025 |
| DBG Social Ltd | Information & communication | 2025 |
| Dcutilities NE Limited | Energy | 2022 |
| Dean Cullen Drywalling Limited | Construction | 2016 |
| Dean Hunter Kitchens Limited | Construction | 2014 |
| Deco Trophies and Engraving Limited | Other services | 1961 |
| Deerness Valley Dairy Limited | Agriculture & fishing | 2020 |
| Dell Roofing Services Limited | Construction | 2017 |
| Dene Valley Community Partnership | Other services | 2003 |
| Dene Valley Community Transport Ltd | Other services | 1999 |
| Denemouth Caravan Park Limited | Arts & recreation | 2005 |
| Deovia Ltd | Transport & logistics | 2025 |
| Derwent Osteopathy Ltd | Health & social care | 2014 |
| Design by Kinship Ltd | Professional & scientific | 2012 |
| Design Innovations Workshop Limited | Professional & scientific | 2020 |
| Devon Camper Conversions Ltd | Manufacturing | 2026 |
| Devro Recruitment Ltd | Administrative & support | 2025 |
| Dewberrybeaumont Ltd | Professional & scientific | 2008 |
| DFC Resources, Aggregates and Recycling Ltd | Wholesale & retail | 2017 |
| DG Pipefitting Ltd | Mining & quarrying | 2014 |
| DH Drawings Design and Build Services Limited | Professional & scientific | 2008 |
| Dhdg (NE) Limited | Construction | 2020 |