| Sketchplay Ltd | Professional & scientific | 2025 |
| SLD Planning Ltd | Construction | 2016 |
| Sleepwell Limited | Wholesale & retail | 1956 |
| Slingley Fields Management Company Ltd | Extraterritorial | 2019 |
| Smart Barber Sunderland Ltd | Other services | 2025 |
| Smart Manufacturing Solutions Consultancy Ltd | Information & communication | 2021 |
| Smart Manufacturing Solutions Ltd | Administrative & support | 2020 |
| Smart Manufacturing Solutions Recruitment Ltd | Administrative & support | 2024 |
| Smart Manufacturing Solutions Systems Ltd | Information & communication | 2024 |
| Smart Manufacturing Solutions Technology Ltd | Information & communication | 2021 |
| Smart ORM Consulting Ltd | Professional & scientific | 2025 |
| Smart Property Solutions North East Ltd | Real estate | 2020 |
| Smile Wide Together C.I.C. | Health & social care | 2022 |
| Smul Consultants Ltd | Professional & scientific | 2021 |
| SNG (Seaham) Limited | Hospitality | 2025 |
| SO (Hexham) Limited | Hospitality | 2025 |
| Solo Engineering North East Limited | Other services | 2024 |
| Solo Properties (North East) Limited | Real estate | 2015 |
| Sonach Marine Limited | Transport & logistics | 2020 |
| Sora Living Limited | Real estate | 2022 |
| Sparkledevelop Limited | Administrative & support | 2021 |
| Specialized Blasting & Coatings Limited | Manufacturing | 2007 |
| Spectrum 5 Holdings Ltd | Real estate | 2023 |
| SPF Inspection Ltd | Mining & quarrying | 2020 |
| ST. Astier Limited | Construction | 2003 |
| Start and Go Fitness Ltd | Arts & recreation | 2025 |
| Starz Drama School Limited | Arts & recreation | 2025 |
| Starz Performers Academy C.I.C. | Arts & recreation | 2025 |
| Station Road Service Centre Ltd | Wholesale & retail | 2025 |
| STEELWORKS55 Ltd | Other services | 2018 |
| Stephen Lamb Ltd | Professional & scientific | 2025 |
| Steve Ryan Residential Limited | Real estate | 2023 |
| Steve's Driver Cover Ltd | Transport & logistics | 2007 |
| Stirling Foods Limited | Extraterritorial | 2015 |
| Stirling Meats Limited | Manufacturing | 2004 |
| Stone Scout Property Limited | Administrative & support | 2025 |
| Stonehill Trading Limited | Other services | 2020 |
| Storybook Flowers Ltd | Wholesale & retail | 2025 |
| Strange Motorsport Ltd | Manufacturing | 2021 |
| Strata Cost Consultancy Limited | Professional & scientific | 2025 |
| Stream Automotive (Teesside) Ltd | Wholesale & retail | 2025 |
| Strides IT Services Ltd | Information & communication | 2022 |
| STY Properties Limited | Real estate | 2025 |
| Stylecall Limited | Professional & scientific | 1992 |
| Subport (Durham) Limited | Construction | 2024 |
| Sugar Mill Properties Limited | Real estate | 2001 |
| SUI Cura Ltd | Other services | 2025 |
| Sun Indian Curry Limited | Hospitality | 2022 |
| Sweet Cuddles Co Ltd | Wholesale & retail | 2025 |
| Swyftly Logistics Limited | Transport & logistics | 2025 |
| Sylvainent Ltd | Wholesale & retail | 2025 |
| T S Auto Services North East Ltd | Wholesale & retail | 2024 |
| T T Coatings (Durham) Limited | Manufacturing | 2022 |
| T T Coatings Limited | Wholesale & retail | 2012 |
| T5 Product Distribution Limited | Administrative & support | 2009 |
| TCY Travel Ltd | Transport & logistics | 2025 |
| Technalight Ltd | Construction | 2026 |
| Temex Electrical Ltd | Manufacturing | 2021 |
| Tempest Rope Access Solutions Limited | Construction | 2023 |
| TFT Fighter Management Ltd | Real estate | 2023 |
| TFT MMA Ltd | Arts & recreation | 2020 |
| THE 4B Group Limited | Financial services | 2023 |
| THE Actors Forge Academy Ltd | Education | 2025 |
| THE Actors Forge Limited | Administrative & support | 2019 |
| THE Avenu OFF License Limited | Wholesale & retail | 2025 |
| THE Canny Candy Gadgies Limited | Wholesale & retail | 2019 |
| THE Creative Virtual Assistant Limited | Administrative & support | 2023 |
| THE Lifeline Support Network Ltd | Professional & scientific | 2025 |
| THE Little Refill Shop Ltd | Wholesale & retail | 2019 |
| THE Metryx Group Limited | Professional & scientific | 2025 |
| THE Mill Inn Seaham Ltd | Hospitality | 2025 |
| THE North East Military Vehicle Club Ltd | Other services | 2002 |
| THE Northern Lass Lounge Ltd | Administrative & support | 2023 |
| THE Ranch Seaham Ltd | Hospitality | 2018 |
| THE Sea WE SEE CIC | Professional & scientific | 2024 |
| THE Secret Garden Wellness Co Ltd | Other services | 2025 |
| THE Smith Camera COY Limited | Information & communication | 2007 |
| THE Sunbed Shop Seaham Ltd | Other services | 2024 |
| THE Sweatbox Seaham Limited | Arts & recreation | 2017 |
| THE Taxi Company (Murton) Limited | Transport & logistics | 2009 |
| THE Times Inn GUN Club Limited | Arts & recreation | 2010 |
| THE Trifix Group Limited | Manufacturing | 2018 |
| THE Unique Bathroom Company (NE) Limited | Construction | 2018 |
| THE Very Top Ltd | Professional & scientific | 2026 |
| Thermal Transfer Limited | Financial services | 2004 |
| Thomas Garage Ltd | Wholesale & retail | 2022 |
| Thomas Motors Ltd | Wholesale & retail | 2024 |
| Three Rivers Health & Safety Consultancy Limited | Professional & scientific | 2020 |
| Time & O Ltd | Information & communication | 2023 |
| Tizard Roofing Ltd | Construction | 2026 |
| Tizard's Ltd | Other services | 2019 |
| TLM Home Innovations Ltd | Construction | 2021 |
| TMH Projects Ltd | Real estate | 2024 |
| Tommy Franks Limited | Wholesale & retail | 2023 |
| Tonks & Company (Easington Lane) Limited | Other services | 1942 |
| Top Dog Car Care Limited | Administrative & support | 2026 |
| Torna Ltd | Hospitality | 2026 |
| Total Site Solutions NE Limited | Administrative & support | 2025 |
| Totus Tuus Ltd | Administrative & support | 2025 |
| Traiteconomy Ltd | Information & communication | 2025 |