| Document Logic Limited | Wholesale & retail | 2002 |
| Doggy Access Limited | Construction | 2017 |
| Dogodo Limited | Wholesale & retail | 2026 |
| Dogwood Adventure Play Ltd | Other services | 2018 |
| Done Right Roofing Services Ltd | Construction | 2022 |
| Done Right Roofing UK Ltd | Construction | 2023 |
| Donna Sandall Family Law Ltd | Professional & scientific | 2025 |
| Donnelly Engineering & Commissioning Limited | Professional & scientific | 2019 |
| Doris & VI Ltd. | Financial services | 2013 |
| Dormel Limited | Administrative & support | 2000 |
| Dorserve Limited | Construction | 2008 |
| Doryan Trans Ltd | Transport & logistics | 2020 |
| Dough Bros Pizzeria Ltd | Hospitality | 2019 |
| Doughlicious Darlington Limited | Hospitality | 2025 |
| Douglas Tyre and Autocare Limited | Wholesale & retail | 2018 |
| Dovetail Joinery & Building Services Ltd | Construction | 2020 |
| DOW Consulting Ltd | Professional & scientific | 2025 |
| DOW Developments Ltd | Construction | 2021 |
| Down Range Ltd | Arts & recreation | 2023 |
| Downing Dance Academy Limited | Arts & recreation | 2019 |
| DP Electrical (North East) Limited | Construction | 2026 |
| DP Green Properties Ltd | Real estate | 2021 |
| DP3 Technology Ltd | Information & communication | 2011 |
| Dpdb Properties Ltd | Real estate | 2025 |
| Dpdp Properties Limited | Real estate | 2022 |
| DPM Consultants Ltd | Professional & scientific | 2021 |
| Dpndt Ltd | Professional & scientific | 2022 |
| DR Kitson Teledermatology Ltd | Health & social care | 2020 |
| DR Loulittle Locum Services Ltd | Professional & scientific | 2025 |
| DR Teeth Whitening Darlington Ltd | Other services | 2022 |
| Dragon Place (Darlington) Ltd | Hospitality | 2019 |
| Dragon Slayer Distillery Limited | Manufacturing | 2013 |
| Drawingdesk Marine Ltd | Information & communication | 2026 |
| Dream Ments Limited | Wholesale & retail | 2025 |
| Dream Play Events UK Ltd | Administrative & support | 2024 |
| Dream Property Investments Ltd | Real estate | 2019 |
| Dream SKN Ltd | Other services | 2024 |
| Dream SKN Training Ltd | Education | 2025 |
| Dreamy Beginnings Ltd | Arts & recreation | 2024 |
| Dresco Health and Aesthetics Ltd | Health & social care | 2023 |
| Dresco Healthcare Ltd | Health & social care | 2026 |
| Drewfix Ltd | Wholesale & retail | 2025 |
| Drifthall Ltd | Arts & recreation | 2021 |
| Drinksmate Eco Cups Ltd | Manufacturing | 2025 |
| Drishti Imaging Ltd | Health & social care | 2018 |
| Drive Around Limited | Transport & logistics | 2015 |
| Drive Safe Academy Ltd | Education | 2026 |
| Drive-Mac Ltd | Construction | 2024 |
| Driveway Surfacing Plus Ltd | Construction | 2022 |
| Drizzel 2020 Ltd | Hospitality | 2020 |
| DRM Epoxy Pro Solutions Limited | Construction | 2023 |
| Dronecam Solutions Limited | Professional & scientific | 2016 |
| DRS Surfacing Ltd | Construction | 2019 |
| Drsc Publishers Ltd | Information & communication | 2015 |
| DRUGLAB118 Ltd | Manufacturing | 2013 |
| DS Electrical Solutions Ltd | Construction | 2024 |
| DS Suction Excavation Ltd | Construction | 2025 |
| DS Telecommunications Ltd | Information & communication | 2024 |
| DSB Fleet Ltd | Transport & logistics | 2025 |
| DSJ Property Maintenance Ltd | Construction | 2024 |
| DSL62 Ltd | Real estate | 2025 |
| DSM CAM Limited | Other services | 2024 |
| DSM N.E. Ltd | Manufacturing | 1994 |
| DT Roadways Ltd | Construction | 2019 |
| DTC Entertainment Group Ltd | Arts & recreation | 2026 |
| Dufell Roofing Company Limited | Construction | 1972 |
| Duffill E-Commerce Ltd | Wholesale & retail | 2023 |
| Duncan Oneil Limited | Information & communication | 2016 |
| Duncans Property Lettings Ltd | Real estate | 2020 |
| Dunhouse Quarry Co.Limited | Mining & quarrying | 1954 |
| Durham Cabins Ltd | Administrative & support | 2026 |
| Durham Compliance Services Limited | Administrative & support | 2012 |
| Durham County Golf Union Ltd | Arts & recreation | 2026 |
| Durham Dance Limited | Administrative & support | 2017 |
| Durham Hygiene Limited | Health & social care | 2014 |
| Durham Logistics (NE) Ltd | Transport & logistics | 2026 |
| Durham Logistics Ltd | Transport & logistics | 2021 |
| Durham Retreats Ltd | Hospitality | 2024 |
| Durham Road Garage Ltd | Wholesale & retail | 2023 |
| Durham Tees Valley Windows, Doors and Conservatories Limited | Construction | 2007 |
| Durham Utilities Ltd | Professional & scientific | 2016 |
| Dutton Greenstreet Properties Limited | Real estate | 2015 |
| Dv-Ola Properties Ltd | Hospitality | 2019 |
| DVD Projects Ltd | Professional & scientific | 2019 |
| Dvgmi Properties LLP | | 2020 |
| DW Flooring Darlington Ltd | Construction | 2015 |
| DW LGS Ltd | Administrative & support | 2025 |
| DWB Overseas Investments Limited | Financial services | 2023 |
| Dynamic Blue Composites Limited | Manufacturing | 2025 |
| Dynamic Wall Printing Ltd | Manufacturing | 2024 |
| Dziewonski Transport Limited | Transport & logistics | 2014 |
| E & D Logistical Ltd | Transport & logistics | 2025 |
| E & K Doshi Limited | Real estate | 2019 |
| E N Metcalfe & SON Limited | Real estate | 1996 |
| E Tackle Ltd | Wholesale & retail | 2025 |
| E&L Dance Boutique Limited | Wholesale & retail | 2017 |
| E&T Roofing and Cladding Limited | Construction | 2026 |
| E-Tech Process Limited | Information & communication | 2019 |
| E-Type Developments Limited | Professional & scientific | 2025 |
| E-Type Fabs Ltd | Manufacturing | 2003 |