| Sieniewicz Medical Services Limited | Health & social care | 2023 |
| Sightline Geomatics Limited | Construction | 2016 |
| Silent Revolution Group Ltd | Wholesale & retail | 2024 |
| Silven Business Consulting Limited | Professional & scientific | 2018 |
| Silven Commercial Money Limited | Financial services | 2018 |
| Silven Digital Limited | Administrative & support | 2022 |
| Silver Birch Gardens Management Company Limited | Households | 2020 |
| Silver Sands Holiday Park Ltd | Hospitality | 2023 |
| Silver Ventum (UK) Limited | Construction | 2020 |
| Silverdene Medical Limited | Health & social care | 2022 |
| Simform UK Limited | Professional & scientific | 2006 |
| Simkar Consultants Limited | Professional & scientific | 2026 |
| Simmons Developments (Cornwall) Ltd | Real estate | 2016 |
| Simon Annear Electrical Limited | Construction | 2019 |
| Simon Annear Maintenance Limited | Construction | 2024 |
| Simon Annear Plumbing and Heating Ltd | Construction | 2007 |
| Simon Grant Building Ltd | Construction | 2019 |
| Simon Hocking Holding Limited | Financial services | 2013 |
| Simon Willoughby Limited | Professional & scientific | 2016 |
| Sitespeak Ltd | Information & communication | 2025 |
| Sivis Logistics Ltd | Transport & logistics | 2022 |
| Sixty Acres Farm Limited | Agriculture & fishing | 2010 |
| SJ Chesworth Ltd | Arts & recreation | 2017 |
| SJD Kitchens Limited | Construction | 2022 |
| Sjgoh Limited | Health & social care | 2013 |
| SJS Developments SW Ltd | Construction | 2022 |
| Skal Drinks SA Ltd | Wholesale & retail | 2019 |
| Skal Limited | Professional & scientific | 2016 |
| SKB Sails Limited | Manufacturing | 2004 |
| Skyepastapins Ltd | Information & communication | 2026 |
| Skyla Trading Company Ltd | Wholesale & retail | 2025 |
| SL Tradings (PVT) Ltd | Wholesale & retail | 2026 |
| Slab Developments Limited | Construction | 2024 |
| SLC Enterprises Ltd | Information & communication | 2023 |
| Sleeklight Ltd | Manufacturing | 2013 |
| Sloth Productions Ltd | Information & communication | 2020 |
| Sloth Studios Ltd | Wholesale & retail | 2023 |
| SM Auto Tech Limited | Wholesale & retail | 2026 |
| SM HR Consulting Ltd | Administrative & support | 2013 |
| Smart Ocean Technology UK Limited | Information & communication | 2024 |
| Smartcitizen Limited | Professional & scientific | 2003 |
| Smbw Consulting Ltd | Professional & scientific | 2025 |
| SMG UK Translations Limited | Professional & scientific | 2012 |
| Smile Together Commercial Limited | Real estate | 2017 |
| Smile Together Dental CIC | Health & social care | 2012 |
| Smoothsailmvp Ltd | Professional & scientific | 2024 |
| SMS Carpentry and Building Limited | Construction | 2022 |
| Snowball Foundry Ltd | Information & communication | 2013 |
| Soaring Stem Ltd | Professional & scientific | 2021 |
| Soarns Shepherds Huts Ltd | Hospitality | 2021 |
| Social Economy and Co-Operative Development Cornwall Limited | Information & communication | 1997 |
| Sokipling Limited | Manufacturing | 2020 |
| SOL Collective UK Ltd | Arts & recreation | 2026 |
| Solaque Ltd | Manufacturing | 2024 |
| Solis CG Ltd | Administrative & support | 2020 |
| Sollyo Intelligence Limited | Information & communication | 2026 |
| Something Ellse Limited | Financial services | 2013 |
| Soon to BE MEN Ltd | Education | 2025 |
| Sophie's Art Supplies Ltd | Wholesale & retail | 2017 |
| Soul Sweats Ltd | Other services | 2019 |
| Sound Mortgages Limited | Financial services | 2018 |
| Soundwave Music Limited | Wholesale & retail | 2022 |
| Source Development (Cornwall) Limited | Construction | 2010 |
| Sourdough TIM Ltd | Manufacturing | 2019 |
| South Crofty Limited | Mining & quarrying | 2007 |
| South East Mediation & Law Ltd | Professional & scientific | 2003 |
| South Molton Block Company Limited | Manufacturing | 2013 |
| South Shore Seaton Ltd | Construction | 2020 |
| South Shore Seaton Management Company Limited | Households | 2022 |
| South West Electrical Hire Ltd | Administrative & support | 2015 |
| South West Home Show Limited | Administrative & support | 2016 |
| South West Installations Ltd | Construction | 2024 |
| South West Investment Group (Capital) Limited | Administrative & support | 1989 |
| South West Investment Group Limited | Financial services | 1990 |
| South West Oral Health Limited | Health & social care | 2006 |
| South West Restaurants Limited | Hospitality | 2024 |
| South West Skills Academy Limited | Education | 2014 |
| South West Smart Applications Limited | Other services | 2010 |
| South West Tech Ltd | Manufacturing | 2026 |
| South West Telecommunications Ltd | Information & communication | 2017 |
| South West Therapy Ltd | Health & social care | 2021 |
| South West Window Maintenance Limited | Construction | 2013 |
| Southleigh Management Company (Truro) Limited | Households | 1978 |
| Southwest Bars & Events Limited | Hospitality | 2015 |
| Southwest Cornwall Properties Limited | Real estate | 2024 |
| Southwest Inspections Ltd | Construction | 2021 |
| Southwest Maintenance Ltd | Real estate | 2019 |
| Southwest OIL Heating Specialists Ltd | Construction | 2014 |
| Soweni Limited | Education | 2018 |
| Sowenna Construction Limited | Construction | 2024 |
| Sowenna Developments Limited | Construction | 2017 |
| Space Chart Limited | Professional & scientific | 2004 |
| Space Professionals Ltd | Professional & scientific | 2019 |
| Space Tiger Studio Limited | Arts & recreation | 2026 |
| Spacebays Limited | Real estate | 2023 |
| Spaja Limited | Real estate | 2011 |
| Spangross Limited | Real estate | 1976 |
| Spanview UK Limited | Construction | 1997 |
| Spark Neuro Rehab Ltd | Public administration | 2020 |
| Spark-Quay Electrical Services Ltd | Construction | 2024 |