| Cwenerpro Ltd | Professional & scientific | 2017 |
| CWS Fabs Ltd | Construction | 2026 |
| Cyber-I Search Solutions Ltd | Administrative & support | 2020 |
| Cyberpal App Limited | Information & communication | 2019 |
| Cyclic Consulting Ltd | Professional & scientific | 2022 |
| Cyents Ltd | Information & communication | 2025 |
| Cynfosec Limited | Information & communication | 2023 |
| Cyupoce Ltd | Wholesale & retail | 2025 |
| D & H Access Ltd | Construction | 2022 |
| D & J Contracts (Cleveland) Limited | Construction | 1989 |
| D a General Store Ltd | Wholesale & retail | 2020 |
| D and G PUB Company Limited | Hospitality | 2011 |
| D B Livery Installations Limited | Professional & scientific | 2015 |
| D B Site Services Limited | Construction | 1998 |
| D France Stonemasonry Limited | Manufacturing | 2005 |
| D G R Interiors Limited | Construction | 2015 |
| D J Developments (North East) Limited | Extraterritorial | 2017 |
| D J Inspections North East Ltd | Professional & scientific | 2022 |
| D J Reynolds Medic Limited | Health & social care | 2022 |
| D P (North East) Developments Limited | Households | 2009 |
| D Priestley Engineering Services Limited | Construction | 2022 |
| D Richardson Holdings Ltd | Financial services | 2025 |
| D Supermarket Ltd | Wholesale & retail | 2026 |
| D W Transport Limited | Transport & logistics | 2000 |
| D Wright Groundworks Ltd | Construction | 2017 |
| D&A Spedition Ltd | Transport & logistics | 2023 |
| D&D Decor Services Ltd | Construction | 2026 |
| D&K Catering NE Ltd | Hospitality | 2024 |
| D&M Coatings LLP | | 2025 |
| D. C. C. (Cars) Limited | Wholesale & retail | 2002 |
| D.B.S. Services (NO. 3) Limited | Extraterritorial | 1995 |
| D.H Automotive Repair Ltd | Wholesale & retail | 2022 |
| D.P.H.(Darlington) Limited | Wholesale & retail | 2008 |
| D.S Mclaughlin Limited | Construction | 2013 |
| DA Communications Limited | Information & communication | 2023 |
| DAA Groundworks Limited | Construction | 2026 |
| DAE Autocare Ltd | Wholesale & retail | 2011 |
| Dagg's Home Improvements Ltd | Construction | 2025 |
| Daifort Limited | Other services | 2019 |
| Dairak Limited | Construction | 2017 |
| Daltonn Limited | Wholesale & retail | 2026 |
| Dalts Ltd | Real estate | 2005 |
| Damas Engineering Limited | Professional & scientific | 2023 |
| Damascus Legend Ltd | Hospitality | 2018 |
| Dammytee Natural Limited | Other services | 2024 |
| Dams & Reservoirs Limited | Construction | 2009 |
| Dancewright Studio Ltd | Arts & recreation | 2025 |
| Dandriving Ltd | Transport & logistics | 2025 |
| Danelaw Woodworking Solutions Ltd | Manufacturing | 2025 |
| Danesmoor House Day Nursery Ltd | Education | 2011 |
| Daniel Alessandro Ltd | Professional & scientific | 2026 |
| Daniel Cockett Media Ltd | Information & communication | 2018 |
| Daniel Cockett Property Limited | Real estate | 2026 |
| Daniela Works Ltd | Manufacturing | 2021 |
| Dapper Marketing Group Limited | Other services | 2019 |
| Darclarks Ltd | Administrative & support | 2017 |
| Dark Beans Ltd | Manufacturing | 2026 |
| Dark Corner Limited | Other services | 2014 |
| Dark Town Inns Ltd | Hospitality | 2025 |
| Darley and Dove Ltd | Manufacturing | 2020 |
| Darlington & District Hospice Movement | Health & social care | 1986 |
| Darlington & Northallerton Hair Clinic Limited | Health & social care | 2025 |
| Darlington & Tees Blinds Ltd | Construction | 2026 |
| Darlington 1883 Limited | Arts & recreation | 2012 |
| Darlington 24/7 Limited | Arts & recreation | 2016 |
| Darlington Aggregates Ltd | Wholesale & retail | 2024 |
| Darlington Area Churches Youth Ministry | Other services | 2010 |
| Darlington Arena Limited | Arts & recreation | 2011 |
| Darlington Association on Disability | Health & social care | 2008 |
| Darlington Auto Tech Ltd | Wholesale & retail | 2025 |
| Darlington Bedding Centre Limited(The) | Wholesale & retail | 1979 |
| Darlington BM Ltd | Wholesale & retail | 2018 |
| Darlington Body Repair Ltd | Wholesale & retail | 2025 |
| Darlington Business Centre Ltd | Real estate | 2019 |
| Darlington Business Club Limited | Other services | 2017 |
| Darlington Business Services Limited | Professional & scientific | 2011 |
| Darlington Car Wash Limited | Wholesale & retail | 2023 |
| Darlington Claims Centre Ltd | Financial services | 2010 |
| Darlington Community Carnival | Arts & recreation | 2012 |
| Darlington Cricket and Athletic Club (Trading Subsidiary) Limited | Hospitality | 2016 |
| Darlington Cricket and Athletic Club C.I.C. | Arts & recreation | 2016 |
| Darlington Delicatessen Ltd | Wholesale & retail | 2016 |
| Darlington Diecast Models Ltd | Wholesale & retail | 2020 |
| Darlington Digital Services Ltd | Information & communication | 2025 |
| Darlington Discount Store Limited | Wholesale & retail | 2024 |
| Darlington Driving Lessons Ltd | Education | 2025 |
| Darlington Energy Solutions Ltd | Professional & scientific | 2023 |
| Darlington Engineering Limited | Professional & scientific | 2018 |
| Darlington Eyecare Limited | Wholesale & retail | 2015 |
| Darlington GAS Limited | Construction | 2023 |
| Darlington Gymnastics Club | Arts & recreation | 2013 |
| Darlington Hair & Beauty Ltd | Wholesale & retail | 2023 |
| Darlington Harriers & Athletics Club | Arts & recreation | 2021 |
| Darlington Healthcare Limited | Wholesale & retail | 2023 |
| Darlington Home Care Limited | Health & social care | 2012 |
| Darlington Indoor Bowls Club Limited | Arts & recreation | 2008 |
| Darlington Investment Planning Limited | Extraterritorial | 1996 |
| Darlington K9 RAW Feeds Limited | Wholesale & retail | 2022 |
| Darlington Mind | Health & social care | 2002 |
| Darlington MOT Centre Limited | Extraterritorial | 2025 |