| Star Eiendom Ans | Real estate | 1987 |
| Stene Stål Produkter AS | Manufacturing | 2021 |
| Stenmoen Invest AS | Real estate | 2021 |
| Stern Auto AS | Wholesale & retail | 2016 |
| Stian Bratland AS | Education | 2021 |
| Stimi Holding AS | | 2022 |
| Strandveien 1-3 AS | Real estate | 1996 |
| Strømnesåsen Eiendom AS | Real estate | 2018 |
| Strømstad Glass Og Aluminium AS | Construction | 2006 |
| Stylish Cutz AS | Other services | 2023 |
| Stylist AS | Education | 2025 |
| Suji Holding AS | | 2024 |
| Sunnere Inneklima AS | Wholesale & retail | 2026 |
| Svalestuen Holding AS | Real estate | 2024 |
| Svein André Olsen Holding AS | Education | 2016 |
| Svein Nesøen Holding AS | Construction | 2016 |
| Sveising-Bygg AS | Construction | 2017 |
| Sälvik AS | Real estate | 2020 |
| Sølvi Harjo AS | Education | 2026 |
| Takofa AS | Administrative & support | 2026 |
| Talitor Bygg AS | Construction | 2021 |
| Talitor Construction AS | Construction | 2017 |
| Talitor Electronics AS | Wholesale & retail | 2013 |
| Talitor Holding AS | Construction | 2013 |
| Tannlege Anas Alhaydar AS | Health & social care | 2025 |
| Taxi Østfold AS | Transport & logistics | 1993 |
| Taxisentralen AS | Transport & logistics | 1987 |
| Tej Takst AS | Professional & scientific | 2012 |
| Tejvin AS | Wholesale & retail | 1997 |
| Tek Drift AS | Administrative & support | 2025 |
| Tek Holding AS | Real estate | 2005 |
| Teqton Norway AS | Wholesale & retail | 2007 |
| Testing Product Service AS | Manufacturing | 2018 |
| Thomas Haugen AS | Wholesale & retail | 2025 |
| Thor Consult AS | Information & communication | 2014 |
| THS 24 AS | Administrative & support | 2024 |
| Time 2 Think AS | Professional & scientific | 2019 |
| Tindlund Terrasse AS | Real estate | 2018 |
| Tmcc Holding AS | Real estate | 2019 |
| Tnvia AS | | 2026 |
| Tocco Norge Da | Wholesale & retail | 1997 |
| Tomteveien 51 a AS | Real estate | 2008 |
| Torill Solhøi Ellefsdatter Revisjon Og Regnskap AS | Professional & scientific | 2025 |
| Totalservice 24 AS | Construction | 2012 |
| Tove & Mette Video Da | Administrative & support | 1989 |
| Transcom Norge AS | Administrative & support | 1989 |
| Trening Og Helse AS | Health & social care | 2013 |
| Trestad Sanering & Demontering AB | Construction | 1995 |
| Trirat Thai AS | Hospitality | 2023 |
| Trivsel Eiendom 1 AS | Real estate | 2019 |
| Truebell Norge AS | Wholesale & retail | 2010 |
| Trømborg Eiendom AS | Real estate | 2010 |
| TS Estate AS | Real estate | 2007 |
| Ulf Helliksen Holding AS | Wholesale & retail | 2021 |
| Ullerøy Utvikling AS | Real estate | 2018 |
| Unilab AS | Information & communication | 2025 |
| Unimedic AS | Health & social care | 2005 |
| Uretusjert AS | Professional & scientific | 2015 |
| Ursula Holding AS | | 2021 |
| V&S Invest AS | Financial services | 2007 |
| Vallefjellet Senter Ans | | 1989 |
| Vbu AS | Real estate | 2004 |
| Verkstoppen Boligutvikling AS | Real estate | 2019 |
| Vi Regnskap AS | Professional & scientific | 2020 |
| Vidasbaby AS | Manufacturing | 2025 |
| Viken Bobil AS | Wholesale & retail | 2019 |
| Villheva AS | Manufacturing | 2025 |
| Visma Smartskill AS | Education | 2002 |
| Vitadin AS | Wholesale & retail | 2017 |
| Vitamax AS | Wholesale & retail | 2014 |
| Wentro AS | Financial services | 2016 |
| Wiljea Service AS | Transport & logistics | 2013 |
| Witana AS | Professional & scientific | 2014 |
| X-Wolf AS | Professional & scientific | 2022 |
| Xcallcenter AS | Wholesale & retail | 2024 |
| Yra AS | Professional & scientific | 2023 |
| Ytterstad Consulting AS | Professional & scientific | 2025 |
| Yvenåsen Boligutvikling AS | Real estate | 2019 |
| Åkenes Holding AS | | 2020 |
| Åsebu Sør Vann Og Avløp | Water & waste | 2009 |
| Øivin Fjeld Gitarverksted AS | Other services | 2019 |
| Østfold Blomster AS | Wholesale & retail | 2025 |
| Østfold Spa Og Fritid AS | Wholesale & retail | 2020 |
| Østfold Taxi Regnskap AS | Professional & scientific | 2008 |
| Østfold Tre & Sandblåsing AS | Manufacturing | 2007 |
| Østfold Uteanlegg AS | Construction | 2019 |
| Østfold VVS AS | Construction | 2012 |
| Østfoldhallen Catering AS | Hospitality | 1990 |
| Østfoldhallen Klokker Og Smykker AS | Wholesale & retail | 2015 |
| Østlandet Ventilasjon Og Klima AS | Construction | 2025 |