| S B Roofing & Cladding Limited | Construction | 2006 |
| S Colwell Consultancy Limited | Professional & scientific | 2019 |
| S D Business Services Limited | Professional & scientific | 2011 |
| S Grimes Groundworks Ltd | Construction | 2017 |
| S H & H Teasdale (Durham) Limited | Construction | 2010 |
| S H Holdings (North East) Limited | Financial services | 2022 |
| S Peart Construction Limited | Construction | 2018 |
| S Willoughby Groundworks Limited | Construction | 2015 |
| S. D. Smith Limited | Other services | 2005 |
| S. W. Transport Ltd | Transport & logistics | 2008 |
| S.A.M Solutions 24/7 Ltd | Health & social care | 2013 |
| S.J Woods Plumbing & Heating Limited | Construction | 2007 |
| S.S. Meat Wholesale Limited | Wholesale & retail | 1992 |
| SA Optometry Services Limited | Health & social care | 2016 |
| Sadberge Village Cafe Limited | Hospitality | 2026 |
| Safe & Sustainable Futures Ltd | Professional & scientific | 2014 |
| Safereach Limited | Construction | 2025 |
| Safespace VR Limited | Wholesale & retail | 2018 |
| Sarah Jane Property Ltd | Households | 2019 |
| Sarateanu Ltd | Wholesale & retail | 2026 |
| SAS Compliance Ltd | Professional & scientific | 2025 |
| Savvy Financial Ltd | Professional & scientific | 2012 |
| Saxon Gate (Stamford Bridge) Management Company Limited | Households | 2016 |
| Scepter International UK Limited | Financial services | 2025 |
| School of Dogs Limited | Other services | 2017 |
| Scotro Mechanical NE Ltd | Construction | 2025 |
| Scott Weston Lettings Ltd | Real estate | 2025 |
| Sealcore Technologies Limited | Manufacturing | 2026 |
| Selective Environmental Solutions Limited | Water & waste | 2017 |
| Self Made Studios C.I.C. | Manufacturing | 2017 |
| Sellers Landscaping and Labor Ltd | Information & communication | 2023 |
| SET in Stone (Teesdale) Limited | Construction | 2023 |
| Seven Stages Limited | Financial services | 2012 |
| Seven Stars Private Wealth Limited | Professional & scientific | 2015 |
| SGJ Investments Limited | Financial services | 2022 |
| SGR Pipework Solutions Ltd | Professional & scientific | 2023 |
| Shaws Elite Homes Ltd | Households | 2025 |
| Sheena Miles Care Services Ltd | Health & social care | 2020 |
| Shelley's Barbering Ltd | Professional & scientific | 2021 |
| Sheperds Food & Wine Limited | Wholesale & retail | 2020 |
| Shervington Family Investment Company Ltd | Financial services | 2024 |
| Shield Haulage Contractors Limited | Transport & logistics | 2022 |
| Shield Haulage Limited | Transport & logistics | 2011 |
| Shield Plant Hire Limited | Administrative & support | 2022 |
| Shieldfield Property Holding Ltd | Real estate | 2025 |
| Shiv Property Developments Limited | Construction | 2024 |
| Showcase Blackpool Limited | Arts & recreation | 2023 |
| Showcase Entertainments International Limited | Arts & recreation | 2010 |
| Showcase North West Limited | Arts & recreation | 2023 |
| Showtame Ltd | Wholesale & retail | 2025 |
| Shpg Engineering Limited | Transport & logistics | 2021 |
| Sidebeck Grange Management Company Limited | Real estate | 2016 |
| Siga Holding Limited | Financial services | 2019 |
| Sight Building Limited | Construction | 2019 |
| Sight Construction Limited | Construction | 2009 |
| Signature Fencing and Flooring Systems Europe Limited | Construction | 2010 |
| Signature Systems Group UK Limited | Extraterritorial | 2017 |
| Silverthorn Group Properties Limited | Households | 2019 |
| Silverthorn Security Limited | Administrative & support | 2019 |
| Silverthorn Waste Management Limited | Water & waste | 2019 |
| Simon Bennison Builders Ltd | Construction | 2014 |
| Simoney Commercial Finance Ltd | Financial services | 2018 |
| Simply Rogue Academy Ltd | Education | 2026 |
| Simpson Fuels Limited | Wholesale & retail | 2004 |
| Siraha Ltd | Financial services | 2023 |
| Sjss Catering Limited | Hospitality | 2021 |
| SJW Films Ltd | Information & communication | 2010 |
| SJW Property Collective Ltd | Real estate | 2026 |
| Sjxs Technology Ltd | Information & communication | 2024 |
| SK Catering (Hamsterley) Limited | Hospitality | 2020 |
| SK Construction (NE) Ltd | Construction | 2023 |
| SK Division Limited | Wholesale & retail | 2025 |
| SKG Joinery Services Limited | Construction | 2015 |
| Skillcore NE Limited | Other services | 2025 |
| Skin Solutions Oxford Limited | Health & social care | 2015 |
| Skogafoss Properties Ltd | Real estate | 2025 |
| Slingsby Close Management Company Limited | Real estate | 2021 |
| SLJ Projects Limited | Professional & scientific | 2007 |
| Smallbone Kitchens Ltd | Construction | 2011 |
| Smith Fish and Chips Limited | Hospitality | 2019 |
| Smithjw Couriers Ltd | Transport & logistics | 2026 |
| SMW Engineering Ltd | Manufacturing | 1994 |
| SO Unique (Darlington) Limited | Wholesale & retail | 2023 |
| SO Unique Garden and Furniture Darlington Ltd | Wholesale & retail | 2026 |
| Solace Resolutions Ltd | Professional & scientific | 2026 |
| Solar EVO Ltd | Construction | 2022 |
| Some Beans Limited | Hospitality | 2024 |
| Sones Driveways Ltd | Construction | 2016 |
| Songpad Limited | Information & communication | 2022 |
| Sorento Takeaway (NE) Limited | Hospitality | 2023 |
| Soul Aspect Ltd | Administrative & support | 2022 |
| South Durham Draughting Ltd | Professional & scientific | 2002 |
| South Durham Enterprise Agency Limited | Administrative & support | 1987 |
| South Durham Gymnastics Club Limited | Education | 2023 |
| South Durham Honey Ltd | Wholesale & retail | 2016 |
| South Durham Leisure Limited | Arts & recreation | 2006 |
| South Durham Structures Limited | Construction | 1981 |
| South West Durham Business Centre Limited | Real estate | 2016 |
| South West Durham Properties Ltd | Real estate | 2015 |
| Spark Public Sector Solutions Ltd | Professional & scientific | 2023 |