| Sight (Durham) Limited | Health & social care | 1986 |
| Sign Lead Ltd | Manufacturing | 2019 |
| Siguren Technologies Limited | Information & communication | 2006 |
| Siloteq Limited | Wholesale & retail | 2013 |
| Silver Shoes Limited | Professional & scientific | 2024 |
| Simon Barningham Ltd | Wholesale & retail | 2018 |
| Simply Additions Ltd | Professional & scientific | 2004 |
| Simply Sparkling North East Ltd | Administrative & support | 2026 |
| Sinch Consultancy Services Ltd | Professional & scientific | 2025 |
| Singular Security Ltd | Construction | 2025 |
| SJ Bailey Engineering Limited | Professional & scientific | 2022 |
| SJ Bespoke Ltd | Construction | 2022 |
| SJB Cleaning Services NE Ltd | Administrative & support | 2020 |
| SJE Management Services Ltd | Professional & scientific | 2026 |
| Skaldborn Ltd | Wholesale & retail | 2025 |
| Skipsandbins.Com Limited | Water & waste | 2008 |
| SLM Construction Consultancies Limited | Construction | 2015 |
| SM Comedy Limited | Arts & recreation | 2010 |
| Smartcraft Software UK Limited | Information & communication | 2012 |
| Smash Group Limited | Professional & scientific | 2022 |
| SMB BIM Services Ltd | Professional & scientific | 2026 |
| SMC Wind Turbine Tech Ltd | Construction | 2025 |
| Smith's Leisure Limited | Arts & recreation | 2018 |
| Smoky Grill Limited | Hospitality | 2025 |
| SNS Cycling CIC | Health & social care | 2024 |
| Social Enterprise Acumen CIC | Professional & scientific | 2010 |
| Social Enterprise Places North East CIC | Other services | 2023 |
| Soil Haulage & Industrial Transport Ltd | Water & waste | 2025 |
| Solana (NE) Limited | Energy | 2025 |
| Solar Advanced Systems Ltd | Construction | 2009 |
| Sorella Hair & Beauty Salon Ltd | Other services | 2022 |
| Sorriso Cafe Houghton Limited | Hospitality | 2025 |
| South Durham Events Limited | Hospitality | 2025 |
| South Durham Refrigeration Limited | Extraterritorial | 2008 |
| South Yorkshire Cars Limited | Wholesale & retail | 2017 |
| Sparkling Touch Limited | Administrative & support | 2025 |
| Special Iapps C.I.C. | Education | 2011 |
| Specialised Event Catering Ltd | Hospitality | 2019 |
| Spiceway Ltd | Hospitality | 2025 |
| Spire Carpet Cleaning N.E Ltd | Administrative & support | 2024 |
| SPN Professional Services Limited | Professional & scientific | 2014 |
| Spring Chop House Limited | Hospitality | 2026 |
| Springwell Energyfarm Limited | Energy | 2021 |
| Spurdeck Limited | | 1976 |
| SR Stores Ltd | Wholesale & retail | 2023 |
| SRJ Energy Ltd | Wholesale & retail | 2014 |
| SRJ Forecourts Ltd | Real estate | 2023 |
| SRJ Superstores Ltd | Wholesale & retail | 2023 |
| Ssms Ltd | Health & social care | 2021 |
| ST Consult (NE) Limited | Professional & scientific | 2023 |
| ST Georges Properties (North East) Limited | Real estate | 2020 |
| Standard Issue Magazine Ltd | Extraterritorial | 2014 |
| Stark Industries N.E. Limited | Information & communication | 2018 |
| Startmaze Limited | Wholesale & retail | 1987 |
| Stealth Barbers Ltd | Other services | 2025 |
| Stokes Fabrication Limited | Manufacturing | 2025 |
| Stonebridge Restoration Limited | Real estate | 2019 |
| Stonebridge Roofing & Building Limited | Construction | 2024 |
| Straloch Estates Limited | Real estate | 2002 |
| Streetnature Property Holdings Ltd | Hospitality | 2025 |
| Stu's Camping Shack Ltd | Wholesale & retail | 2023 |
| Studio Burn Fitness C.I.C. | Arts & recreation | 2019 |
| Studio V (NE) CIC | Arts & recreation | 2023 |
| Styan Limited | Financial services | 2019 |
| Suburban Clothing Ltd | Wholesale & retail | 2024 |
| Sugoi Consulting Limited | Other services | 2021 |
| Sun Prices Mark Retailer Ltd | Wholesale & retail | 2025 |
| Sun Spirit (Lspv) Limited | Energy | 2012 |
| Sunflowers and Smiles Counselling Ltd | Financial services | 2025 |
| Sustain 3D Limited | Construction | 2013 |
| Sustainable Business Services Ltd | Professional & scientific | 2020 |
| Sweet Factory Arts & Crafts Ltd | Wholesale & retail | 2020 |
| Swells Commercial Trading Ltd | Wholesale & retail | 2025 |
| Swich Ltd | Professional & scientific | 2003 |
| Swiftsure Networks Ltd | Information & communication | 2024 |
| SWM (NE) Limited | Construction | 2025 |
| Systemfourteen Ltd | Health & social care | 2025 |
| T K Garnham & Sons Ltd | Manufacturing | 2013 |
| T.J.S. Blade Solutions Ltd | Manufacturing | 2018 |
| T.L. Grey (Chemist) Limited | Wholesale & retail | 2002 |
| Taerin Technologies Ltd | Information & communication | 2024 |
| Tambh Ltd | Professional & scientific | 2021 |
| Tangled (Durham) Limited | Other services | 2017 |
| Tasfl Ltd | Education | 2016 |
| Tasty Red House Ltd | Hospitality | 2023 |
| Tattoo House Ltd | Other services | 2021 |
| Tavern Training Company Ltd | Administrative & support | 2018 |
| Taylor’S Farm Developments Ltd | Construction | 2021 |
| Tbax Ltd | Construction | 2012 |
| Teach Last Limited | Administrative & support | 2023 |
| Techfix Phone Limited | Wholesale & retail | 2024 |
| Teem Partners Ltd | Professional & scientific | 2017 |
| Teesside Property Developments CO1 Limited | Construction | 2025 |
| Telco Consult Limited | Information & communication | 2026 |
| Telephone Consultation Services Limited | Professional & scientific | 2009 |
| Telfer Estates Ltd | Real estate | 2025 |
| Tenancy Tech Ltd | Information & communication | 2023 |
| Ternfit Limited | Arts & recreation | 2020 |
| THE Amalfi ( Newbottle ) Ltd | Hospitality | 2021 |
| THE Baked Studio Limited | Hospitality | 2021 |