| Survey Repair UK Ltd | Construction | 2018 |
| Sustainable Eco Solutions Group Limited | Professional & scientific | 2021 |
| Sustainable Oakenshaw SPV Limited | Energy | 2012 |
| Sustainable Solutions (NE) Ltd | Wholesale & retail | 2015 |
| Sutherland Private Clients Ltd | Professional & scientific | 2022 |
| SVK Store Limited | Wholesale & retail | 2025 |
| SW & SON Recycle Limited | Transport & logistics | 2025 |
| SW Distillers Limited | Wholesale & retail | 2021 |
| Swale CC Ltd | Manufacturing | 2023 |
| Swandene Limited | Manufacturing | 2009 |
| SWB Construction NE Limited | Construction | 2019 |
| SWB Properties NE Ltd | Real estate | 2026 |
| Sweet and Spices Durham Ltd | Manufacturing | 2020 |
| Sweet Gains Nutrition Ltd | Hospitality | 2017 |
| Sweet Treat Durham Ltd | Wholesale & retail | 2017 |
| Sweet Treats R US Ltd | Hospitality | 2025 |
| Sweetfry Ltd | Wholesale & retail | 2019 |
| Sweethart Ltd | Hospitality | 2016 |
| Sweetpea Estates Ltd | Real estate | 2024 |
| Swift Key Auto Locksmith Limited | Administrative & support | 2026 |
| Swiftbay Global Ltd | Wholesale & retail | 2025 |
| Swiftbroon Ltd | Wholesale & retail | 2026 |
| Swinburne Maddison LLP | | 2010 |
| Swingfit Dance Limited | Education | 2018 |
| Swingfit Dance Training Limited | Education | 2022 |
| Switch for Sport Ltd | Administrative & support | 2025 |
| SWS Homes Limited | Real estate | 2006 |
| Sycamore Homes Durham Ltd | Real estate | 2022 |
| SYD Varley Groundworks Ltd | Construction | 2018 |
| Sylora Global Ltd | Wholesale & retail | 2025 |
| Symonne Sexton Ltd | Wholesale & retail | 2025 |
| Symphony Psychology Ltd | Health & social care | 2017 |
| Symphony Sports Ltd | Arts & recreation | 2020 |
| Synapptic Ltd | Information & communication | 2012 |
| Syncurasim Ltd | Information & communication | 2026 |
| Synnola Limited | Professional & scientific | 2017 |
| Synovis Technology Limited | Information & communication | 2025 |
| Sysdac Limited | Information & communication | 2004 |
| T - H Nails and Spa Ltd | Other services | 2025 |
| T B Patterson Associates Limited | Financial services | 1985 |
| T Bryan Groundworks Ltd | Construction | 2023 |
| T D Smith & SON Limited | Agriculture & fishing | 1976 |
| T H Production Services Limited | Manufacturing | 2007 |
| T J D Properties Limited | Real estate | 1998 |
| T Jefford Garden Services Ltd | Administrative & support | 2023 |
| T M Construction (NE) Limited | Construction | 2014 |
| T M Ward Transport Limited | Manufacturing | 2020 |
| T&A Drywall Limited | Construction | 2026 |
| T&F Drywall Specialists Ltd | Construction | 2020 |
| T&S Brickwork Ltd | Construction | 2021 |
| T&T Nails Spa Ltd | Other services | 2025 |
| T-Street (Wholesale) Ltd | Wholesale & retail | 2008 |
| T-Tish Ltd | Health & social care | 2023 |
| T.D. Morton Limited | Health & social care | 2003 |
| T.H.K Durham Ltd | Hospitality | 2024 |
| T.Q.K. Limited | Manufacturing | 2002 |
| T.W. Steam & Heating Services Limited | Construction | 1974 |
| T2 Battery Storage Ltd | Energy | 2022 |
| Taham Global Ltd | Wholesale & retail | 2025 |
| Tailored Thinking Limited | Professional & scientific | 2017 |
| Tait Property Developments Ltd | Construction | 2019 |
| Tale Adigozalov Ltd | Wholesale & retail | 2022 |
| Talent Scout Group Ltd | Administrative & support | 2025 |
| Talionis Limited | Professional & scientific | 2012 |
| Tally HO Estates Ltd | Real estate | 2022 |
| Tally HO Estates Management Ltd | Construction | 2024 |
| Tamays Trading Ltd | Wholesale & retail | 2025 |
| Tame Your Technology Limited | Wholesale & retail | 2013 |
| Tamiji Limited | Information & communication | 2024 |
| TAN Transport Ltd | Transport & logistics | 2025 |
| Tandel Properties Ltd | Real estate | 2026 |
| Tandoori Durham Restaurant Ltd | Hospitality | 2023 |
| Tanning Hub Limited | Other services | 2024 |
| Tanzanite Durham Limited | Real estate | 2020 |
| Tapiomedia Limited | Professional & scientific | 2023 |
| Tapstone Ltd | Real estate | 2005 |
| Tarin Ltd | Health & social care | 2025 |
| Tarka Limited | Administrative & support | 1999 |
| Tarmacadams Surfacing Ltd | Construction | 2020 |
| Tarren Golf Ltd | Arts & recreation | 2021 |
| Taste of Durham Ltd | Hospitality | 2025 |
| Tasty Chois Limited | Hospitality | 2024 |
| Tax Apps Limited | Information & communication | 2011 |
| Tax Smart Motors Limited | Financial services | 2025 |
| Taxi Sales UK Limited | Financial services | 2006 |
| Taylor Care Training Limited | Education | 2024 |
| Taylor Home Design Limited | Construction | 2010 |
| Taylor's Bakery Limited | Manufacturing | 1995 |
| Taylor's News Ltd | Wholesale & retail | 2019 |
| TB Payroll Limited | Professional & scientific | 2025 |
| TC Construction North East Ltd | Construction | 2019 |
| TCH (Acquisitions) Limited | Financial services | 2026 |
| TDJ Services Ltd | Professional & scientific | 2013 |
| Tdunn Courier Service Ltd | Transport & logistics | 2025 |
| TE Mata Consulting Limited | Professional & scientific | 2015 |
| Tech DEC Ltd | Construction | 2024 |
| Tech Developer Hub Ltd | Wholesale & retail | 2025 |
| Technical Air Systems (TAS) Ltd | Wholesale & retail | 2025 |
| Technical Asset Solutions Ltd | Other services | 2013 |
| Techplast Ltd | Manufacturing | 2019 |