| Stiller Holdings Ltd | Financial services | 2020 |
| Streonshalh Limited | Financial services | 1998 |
| T.A. Plastic Supplies Limited | Wholesale & retail | 1977 |
| T.A.P. Limited | Professional & scientific | 1988 |
| Take a Break Ltd | Administrative & support | 2002 |
| Taylormade Timber Products Ltd | Manufacturing | 1957 |
| Teesdale Consultants Limited | Professional & scientific | 1981 |
| Teesdale Decor & Carpet Centre Ltd | Wholesale & retail | 2001 |
| Teesdale Windows Limited | Other services | 2003 |
| TEP Electrical Distributors Limited | Wholesale & retail | 1950 |
| Tetron Computer Services Limited | Information & communication | 1996 |
| THE King's Church Durham | Other services | 2004 |
| THE Old Brewery Business Centre Limited | Administrative & support | 2004 |
| THE Road Centre Ltd | Other services | 2006 |
| Thermal Transfer Technology Limited | Manufacturing | 1992 |
| Thomas Abdale Limited | Real estate | 1972 |
| TLC Community Services Limited | Health & social care | 2001 |
| Total Results Limited | Information & communication | 2005 |
| Total Tax Solutions Limited | Professional & scientific | 2006 |
| Townson Limited | Wholesale & retail | 2025 |
| Ttaleed Limited | Wholesale & retail | 2026 |
| TYRES2U (NE) Limited | Wholesale & retail | 2007 |
| Usher Refrigeration Services Ltd | Manufacturing | 2002 |
| V O Professional Limited | Administrative & support | 2004 |
| Valentines Restaurant Limited | Hospitality | 2003 |
| Venture House Property Management Company Limited | Real estate | 2001 |
| Vigo Erection Co Limited | | 1968 |
| Village Care Limited | Health & social care | 2002 |
| Vincent Owen Limited | Other services | 2003 |
| Vita Nova NE Ltd | Real estate | 2020 |
| W. M. Groundworks Limited | Wholesale & retail | 1998 |
| Waddington Street Centre Limited | Health & social care | 1988 |
| Walkery Limited | Wholesale & retail | 2025 |
| Walton Industrial Containers Limited | Manufacturing | 1978 |
| Ward Bros Plant Hire Limited | Water & waste | 1971 |
| Ward Bros Skip Hire Limited | Water & waste | 2025 |
| Ward Timber Limited | Manufacturing | 2002 |
| Warrens Lighting Limited | Wholesale & retail | 1997 |
| Wear Valley Women's AID Limited | Hospitality | 1996 |
| Weardale Entertainments Limited | Arts & recreation | 1999 |
| Weelsh Limited | Wholesale & retail | 2025 |
| West Diamonds Ltd. | Wholesale & retail | 2001 |
| Whatton Limited | Wholesale & retail | 2025 |
| Wheatley Hill Old Scouts Club Limited | Arts & recreation | 2000 |
| William John Limited | Wholesale & retail | 2026 |
| Wolf Northern Limited | Administrative & support | 2018 |
| Woodward International Limited | Professional & scientific | 2002 |
| WRA Consultants Limited | Professional & scientific | 2003 |
| WS Group Holdings Limited | Financial services | 2023 |
| Xenosys Limited | Information & communication | 2002 |
| Zenith Growth Limited | Financial services | 2016 |