| Taylor High Voltage Solutions Ltd | Manufacturing | 2025 |
| Tbra Properties Ltd | Real estate | 2020 |
| TDC Energy 24 Ltd | Energy | 2025 |
| Teaching Gadget Ltd | Education | 2021 |
| Technimark Limited | Manufacturing | 2009 |
| Technology Contractors Limited | Wholesale & retail | 2009 |
| Tees Valley Taverns Limited | Hospitality | 2006 |
| Teesdale Accounting (Darlington) Ltd | Professional & scientific | 2019 |
| Teesdale Chiropody and Podiatry Ltd | Health & social care | 2023 |
| Teesdale Community Resources | Arts & recreation | 2011 |
| Teesdale Conservation Volunteers Limited | Water & waste | 2006 |
| Teesdale Consulting Limited | Information & communication | 2020 |
| Teesdale Crane Hire Limited | Construction | 2003 |
| Teesdale Development Company Limited | Administrative & support | 1997 |
| Teesdale Energy Company Ltd | Other services | 2025 |
| Teesdale Glazing Limited | Construction | 2005 |
| Teesdale Limited | Manufacturing | 2011 |
| Teesdale New Build Services Ltd | Construction | 2025 |
| Teesdale Opportunities for Disabled Youngsters Association (Todys) | Arts & recreation | 2003 |
| Teesdale Physiotherapy Limited | Other services | 2007 |
| Teesdale Renewable Fuels Limited | Wholesale & retail | 2014 |
| Teesdale Renewables Ltd | Construction | 2010 |
| Teesdale Rural Roots CIC | Agriculture & fishing | 2026 |
| Teesdale Structures Ltd | Manufacturing | 2022 |
| Teesdale Surfacing (Paving Contractors) Limited | Wholesale & retail | 1986 |
| Teesdale Toys Limited | Wholesale & retail | 2024 |
| TEK Nexus Ltd | Administrative & support | 2025 |
| Tekwen Estate Limited | Real estate | 2024 |
| Terry’S Aviation Services (T.A.S.) Ltd | Professional & scientific | 2012 |
| Test Dummy Ltd | Information & communication | 2023 |
| Teward Bros Ltd | Construction | 2000 |
| TGC (Upper Teesdale) Ltd | Other services | 2011 |
| Thaeon Pharma Company Limited | Wholesale & retail | 2024 |
| THE Auto Barn (NE) Limited | Wholesale & retail | 2020 |
| THE B.E.S.T. Practice (North East) Ltd | Professional & scientific | 2003 |
| THE Bowes Museum | Arts & recreation | 1999 |
| THE Bowes Museum (Enterprises) Limited | Wholesale & retail | 2009 |
| THE Castle Players | Arts & recreation | 1992 |
| THE Coach House @Eggleston Ltd | Hospitality | 2025 |
| THE College of Scent Dogs Limited | Education | 2017 |
| THE Dales Fryer Ltd | Hospitality | 2024 |
| THE Energetics Clinic Limited | Health & social care | 2024 |
| THE Energetics Retreat CIC | Hospitality | 2025 |
| THE Feed Warehouse Ltd | Wholesale & retail | 2011 |
| THE Food Experience by Richard Hickman Ltd | Hospitality | 2024 |
| THE FOX & Hounds (Cotherstone) Limited | Hospitality | 2002 |
| THE Hive Croydon | Education | 2012 |
| THE Inglenook Wine Bar and Merchants Limited | Wholesale & retail | 2024 |
| THE Laurels at Bowes Ltd | Hospitality | 2017 |
| THE Management Coach Ltd | Professional & scientific | 2022 |
| THE Ministry of Scent Ltd | Other services | 2018 |
| THE Niche Editor Ltd | Administrative & support | 2022 |
| THE Pinfold Club Limited | Hospitality | 2017 |
| THE Pony Guide Ltd | Education | 2023 |
| THE Profit Consultancy Limited | Professional & scientific | 1999 |
| THE Rigging Factory Ltd | Arts & recreation | 2015 |
| THE Rural Tribe Ltd | Hospitality | 2026 |
| THE Still House Collective Ltd | Hospitality | 2026 |
| THE Tanning Castle Limited | Other services | 2025 |
| THE Witham Hall Ltd | Arts & recreation | 2009 |
| Thing Controls Ltd | Information & communication | 2020 |
| This IS Wearside Ltd | Arts & recreation | 2024 |
| Thorngate (Apartments) Management Company Limited | Real estate | 2005 |
| Thorngate (Riverside) Management Company Limited | Other services | 2005 |
| Thorpe Farm Centre Limited | Administrative & support | 2006 |
| Tiplady Tanker Services Ltd | Water & waste | 2009 |
| TOM Heys Developments Ltd | Construction | 2019 |
| Tonotopic Record Company Limited | Information & communication | 2015 |
| Total Balance Limited | Health & social care | 2002 |
| Total Oynx Limited | Hospitality | 2011 |
| Townley Estates (UK) Limited | Real estate | 2013 |
| Townley Estates LLP | | 2013 |
| TRADES4CARE Project Community Interest Company | Construction | 2019 |
| Trafalgar Media Services Limited | Information & communication | 2010 |
| Trevor Atkinson & Co Limited | Construction | 2006 |
| Trucks and Tractors Ltd | Wholesale & retail | 2013 |
| Tulloch Wealth Management Limited | Financial services | 2019 |
| Tully's Electrical Engineers & Complete Building Services Ltd | Construction | 2004 |
| U.K. Assessment Services Limited | Extraterritorial | 2008 |
| UK Inkind Psychology Ltd | Health & social care | 2024 |
| Ulls Field Heritage Ltd | Extraterritorial | 2026 |
| Upland Grazing Ltd | Agriculture & fishing | 2025 |
| Upper Echelon Ltd | Professional & scientific | 2023 |
| Upper Teesdale Agricultural Support Services Ltd | Information & communication | 2007 |
| Urban Rise Limited | Real estate | 2017 |
| Vagenas Everlasting Flowers Limited | Wholesale & retail | 2021 |
| Vanscription Limited | Administrative & support | 2021 |
| Vault Vending Ltd | Wholesale & retail | 2022 |
| VF Agri Repairs Ltd | Manufacturing | 2020 |
| Vital Pharma Limited | Wholesale & retail | 2015 |
| Vorken Limited | Construction | 2022 |
| Wade Glass Limited | Construction | 2016 |
| Water-Smart-Uk Limited | Water & waste | 2023 |
| Watson Accountants Limited | Professional & scientific | 2025 |
| Weft Atelier Limited | Wholesale & retail | 2022 |
| West Park Realty Ltd | Real estate | 2004 |
| Wewillcookforyou Ltd | Hospitality | 2025 |
| Wilderness Outdoor Education Ltd | Education | 2011 |
| Wildon Estates Ltd. | Construction | 2018 |
| William Peat(Barnard Castle)Limited | Agriculture & fishing | 1956 |