| SS (GBR) EOT Limited | Professional & scientific | 2025 |
| SS (GBR) Limited | Administrative & support | 2025 |
| SS Protection NE Ltd | Administrative & support | 2026 |
| SS44 Ltd | Hospitality | 2024 |
| SSL Property Group Ltd | Real estate | 2025 |
| SSM Trans Ltd | Transport & logistics | 2020 |
| SSP Electrical Limited | Construction | 2023 |
| ST Aidan's Church of England Academy Limited | Education | 2007 |
| ST Clare's Court (Darlington) Management Company Limited | Households | 2019 |
| ST Giles Close (Durham) Maintenance Limited | Households | 1999 |
| ST James' Court Management Company (Darlington) Limited | Households | 2007 |
| ST. Anne's Court (Richmond) Management Company Limited | Households | 2000 |
| ST. Augustine's Parish Club Limited | Arts & recreation | 2000 |
| ST. Cuthbert's Court Residents Association Limited | Households | 1983 |
| ST. Edwin's Pre-School Ltd | Education | 2023 |
| STA Commercials Ltd | Wholesale & retail | 2026 |
| STA Telecoms Ltd | Construction | 2025 |
| Stablers Garage Limited | Wholesale & retail | 2012 |
| Stack-Cup Uk/Europe Ltd | Manufacturing | 2025 |
| Stag Capital Ventures Ltd | Financial services | 2023 |
| Stag Management Group Ltd | Real estate | 2023 |
| Stag Real Estate Ltd | Real estate | 2022 |
| Stage 3 Lifting Limited | Other services | 2014 |
| Stage One Events Ltd | Administrative & support | 2022 |
| Stainton Developments Ltd | Construction | 2020 |
| Stainton Quarry Ltd | Mining & quarrying | 2008 |
| Stakas Limited | Health & social care | 2022 |
| Stand OUT Safety Ltd | Wholesale & retail | 2025 |
| Standard Industry Limited | Wholesale & retail | 2025 |
| Standard Inspection Ltd | Professional & scientific | 2014 |
| Standout Signage UK Ltd | Professional & scientific | 2025 |
| Stanhope Agricultural Society | Arts & recreation | 2007 |
| Stanhope Court Management Company Limited | Households | 2003 |
| Stanhope Green Ltd | Manufacturing | 2025 |
| Star Express Pizzeria Ltd | Hospitality | 2025 |
| Star of Bengal (Darlington) Limited | Hospitality | 2005 |
| Starfeb Ltd | Information & communication | 2018 |
| Starkco Limited | Financial services | 2018 |
| Starling March Ltd | Professional & scientific | 2021 |
| Starplex Goods Ltd | Wholesale & retail | 2023 |
| Starters & Puds (Tyneside) Limited | | 2009 |
| Station Real Estate Ltd | Real estate | 2025 |
| Stavro Properties Ltd | Real estate | 2022 |
| Staxx Ltd | Hospitality | 2025 |
| Staywod Ltd | Wholesale & retail | 2025 |
| Steadfast Financial Solutions Ltd | Financial services | 2022 |
| Steadfast Wills and Estate Planning Ltd | Other services | 2024 |
| Steel River Cask Investments Ltd | Financial services | 2024 |
| Steiner Airways Limited | Transport & logistics | 2022 |
| Steiner Motion Pictures Limited | Information & communication | 2017 |
| Steiner Studios Limited | Information & communication | 2022 |
| Steiner Universal Studios Limited | Information & communication | 2022 |
| Stejobell Ltd | Construction | 2022 |
| Stepahead Press Ltd | Information & communication | 2022 |
| Stephen a. Sims (Cars) Limited | Wholesale & retail | 1990 |
| Stephen Littlefair Limited | Wholesale & retail | 2025 |
| Stephen Lockey Plumbing and Heating Ltd | Construction | 2017 |
| Stephen Oliver Living Ltd | Construction | 2025 |
| Stephenson & Sons Ltd | Real estate | 2019 |
| Stephentaylorfx Ltd | Transport & logistics | 2026 |
| Stepramp Ltd | Construction | 2013 |
| Steven Bowes Construction Ltd | Construction | 2019 |
| Sticky Fingers Childcare Ltd | Health & social care | 2010 |
| Stig Fasteners Limited | Wholesale & retail | 2016 |
| Stirling Eyecare Limited | Health & social care | 2018 |
| Stocktake People (North) Ltd | Professional & scientific | 2023 |
| Stockton Road Roofing Limited | Construction | 2024 |
| Stoer Advisory Ltd | Professional & scientific | 2023 |
| Stoer Consulting Limited | Professional & scientific | 2015 |
| Stokoe Property Limited | Real estate | 2023 |
| Stondon Storage Willow Tree Farm Ltd. | Real estate | 2006 |
| Stone Technical Services Group Limited | Construction | 2000 |
| Stonecot Car Sales Ltd | Wholesale & retail | 2018 |
| Stonemouse Limited | Construction | 2015 |
| Stoneriver Commercial Limited | Construction | 2021 |
| Stoneriver Holdings Limited | Financial services | 2020 |
| Stoneriver Housing Limited | Construction | 2020 |
| Stoneriver Investments (North East) Limited | Real estate | 2020 |
| Stop N TAN Darlington Ltd | Other services | 2023 |
| Storbree Ltd | Wholesale & retail | 2026 |
| Storefit (UK) Limited | Construction | 2015 |
| Storey Wholesale Ltd | Wholesale & retail | 2023 |
| Story and Spoon Publishing Limited | Health & social care | 2024 |
| Stove & Fireplace Centre Ltd | Construction | 2019 |
| Stow & Co Properties Ltd | Real estate | 2019 |
| Straight Edge Building Solutions Ltd | Construction | 2024 |
| Straight UP Scaffolding and Roofing Limited | Construction | 2025 |
| Straight UP Scaffolding Services Ltd | Construction | 2021 |
| Straightbooks Ltd | Professional & scientific | 2025 |
| Straker Properties Ltd | Real estate | 2016 |
| Strange Engine Solutions Ltd | Information & communication | 2014 |
| Strathmore Renewables Ltd | Energy | 2013 |
| Stratitech Inc Ltd | Wholesale & retail | 2011 |
| Stratwell Anison Partners Limited | Information & communication | 2025 |
| Streamline E-Commerce Ltd | Wholesale & retail | 2026 |
| Streamlined IT and Training Solutions Limited | Education | 2011 |
| Strelitzia Software Ltd | Information & communication | 2020 |
| Strictly Green Ltd | Wholesale & retail | 2026 |
| Stride Footwear Ltd | Wholesale & retail | 2024 |
| Strive Management Limited | Professional & scientific | 2018 |