| Coulbeck Events Ltd | Education | 2025 |
| Countoak Limited | Extraterritorial | 1987 |
| Countrywide Signs Durham Ltd | Administrative & support | 2022 |
| Coxhoe Electrical Services Limited | Construction | 2010 |
| Coxhoe Service & Supply Limited | Administrative & support | 2023 |
| Coxhoe Service Limited | Administrative & support | 2023 |
| Crafty Mouses Ltd | Manufacturing | 2021 |
| Creative Spaces Durham CIC | Wholesale & retail | 2020 |
| Crest Publishing Ltd | Information & communication | 2024 |
| Crook Hand Car Wash Ltd | Administrative & support | 2019 |
| Cummings Financial Solutions Ltd | Professional & scientific | 2025 |
| Curley Transport Limited | Transport & logistics | 2022 |
| Cutting Edge Reel Services Ltd | Manufacturing | 2020 |
| Cwlx Limited | Arts & recreation | 2025 |
| D Cole Motor Services Limited | Wholesale & retail | 2010 |
| D S Steelworks Ltd | Construction | 2020 |
| D Sands Plumbing & Heating Services Ltd | Construction | 2025 |
| D&D Bar & Hospitality Ltd | Hospitality | 2025 |
| D.K. Steel Erection Limited | Wholesale & retail | 1996 |
| Dacawe Solutions Ltd | Professional & scientific | 2023 |
| Dalton Property Group Ltd | Real estate | 2023 |
| Damascus Road Technical Services Ltd | Arts & recreation | 2009 |
| Daniels Corporation (UK) Limited | Professional & scientific | 2001 |
| Daniels Manufacturing Operations UK Ltd | Manufacturing | 2022 |
| Daniels Rainham Limited | Financial services | 2025 |
| Darling Lettings (NE) Ltd | Real estate | 2025 |
| David a Clark Limited | Construction | 2006 |
| David Alan Simpson Ltd | Extraterritorial | 2024 |
| David Lynn Legal Advice Ltd | Professional & scientific | 2025 |
| Dawson & Hackett Letting Ltd | Real estate | 2020 |
| DB Inspection Limited | Other services | 2022 |
| Debra Chalmers Psychic Medium Limited | Other services | 2011 |
| Delivion Ltd | Wholesale & retail | 2026 |
| Delta November Alpha Ltd | Manufacturing | 2025 |
| Deluxe Improvements Ltd | Administrative & support | 2021 |
| Dent Multi Services Limited | Construction | 2025 |
| Deozze Ltd | Wholesale & retail | 2023 |
| Devil Management Ltd | Other services | 2022 |
| Dex&Fx Ltd | Administrative & support | 2025 |
| Dharker Studios Limited | Information & communication | 2016 |
| DI Stone Masonry Ltd | Manufacturing | 2022 |
| Diamond Clean Group Ltd | Administrative & support | 2023 |
| Divine Atelier Ltd | Other services | 2026 |
| DKR88 Ltd | Wholesale & retail | 2025 |
| DLB Rope Access Ltd | Construction | 2018 |
| Dmtky Limited | Wholesale & retail | 2023 |
| DNA4X4 Ltd | Manufacturing | 2022 |
| Doodl Digital Ltd | Information & communication | 2021 |
| DOP Elevator Co Ltd | Construction | 2024 |
| Douglas Games and Technology Ltd | Information & communication | 2024 |
| Douglas Marks Projects Ltd | Wholesale & retail | 2006 |
| Dragan Consultancy Limited | Education | 2017 |
| Drpg Ltd | Hospitality | 2007 |
| Dsshipment Ltd | Wholesale & retail | 2023 |
| DTF Business Solutions Limited | Professional & scientific | 2025 |
| Duckz Ltd | Transport & logistics | 2023 |
| Dunelm Fine Art Limited | Administrative & support | 2010 |
| Dunelm Optical Co. Limited | Manufacturing | 1973 |
| Dunelm Optical Holdings Limited | Financial services | 2014 |
| Durham & Dales Field Sports Limited | Wholesale & retail | 2022 |
| Durham County Carers Support | Information & communication | 1998 |
| Durham County Vehicle Services Ltd | Wholesale & retail | 2023 |
| Durham Electrics & Fire Ltd | Construction | 2011 |
| Durham Electrics Ltd | Construction | 2022 |
| Durham Fabrication & Laser Ltd | Manufacturing | 2023 |
| Durham Gate (North) Investment Company Ltd | Real estate | 2014 |
| Durham Gate (North) Limited | Real estate | 2014 |
| Durham Gate Limited | Real estate | 1995 |
| Durham Industrial Steam Limited | Manufacturing | 2015 |
| Durham Leasing Limited | Wholesale & retail | 2000 |
| Durham Maintenance Ltd | Wholesale & retail | 2024 |
| Durham Path LLP | | 2023 |
| Durham Skip Hire Limited | Water & waste | 2025 |
| Dutton & Gavin (Textiles) Limited | Wholesale & retail | 1947 |
| Dynamic Portals Limited | Construction | 2023 |
| Earth and Ember Yoga Durham Ltd | Health & social care | 2025 |
| EAS NE Limited | Hospitality | 2022 |
| Eating With the Kids Limited | Wholesale & retail | 2021 |
| Ec&Ma Global Limited | Wholesale & retail | 2026 |
| Eco Cleaning Group Ltd | Administrative & support | 2025 |
| Ecobutler Limited | Professional & scientific | 2023 |
| Edable Art World of Colour Limited | Manufacturing | 2020 |
| Eden View Investments Ltd | Construction | 2020 |
| Edma 1 Ltd | Real estate | 2022 |
| Edwards of Spennymoor Ltd | Real estate | 2018 |
| EJ Sitepro Services Limited | Construction | 2024 |
| EJL Property Developments Ltd | Real estate | 2026 |
| Ekkomec Ltd | Wholesale & retail | 2026 |
| Elbow Properties Limited | Real estate | 2021 |
| Elec NE Ltd | Construction | 2023 |
| Electrotech Building Services Ltd | Construction | 2025 |
| Elevate (North East) Limited | Education | 2025 |
| Elif Trade Ltd | Wholesale & retail | 2025 |
| Elite Construction Training Solutions Ltd | Other services | 2020 |
| Elite Pharma Aesthetics Ltd | Professional & scientific | 2024 |
| Elite UAE Limited | Administrative & support | 2025 |
| Ellem Haytch Ltd | Administrative & support | 2023 |
| Ellie Featherstone BMX Coaching Ltd | Arts & recreation | 2022 |
| Ellipse Surveying Ltd | Professional & scientific | 2022 |
| Ellway Estates Ltd | Real estate | 2017 |