| Saloonius Oy | Hospitality | 2014 |
| Sanimaja Oy | Real estate | 1991 |
| Sanjer Oy | Professional & scientific | 2019 |
| Sara-Boat Oy | Real estate | 2008 |
| Sari ja Juha Leskelä avoin yhtiö | Wholesale & retail | 2012 |
| Satamapalvelu Suvanto Oy | Transport & logistics | 2011 |
| Sawasdee2019 Oy | Wholesale & retail | 2019 |
| Sea Load Control Finland Oy Ltd | Transport & logistics | 1988 |
| SeaFox Kalajoki Oy | Transport & logistics | 2022 |
| Shop By Tiina Oy | Wholesale & retail | 2024 |
| Siermalan Turkis Oy | Agriculture & fishing | 1987 |
| Siikarysä Oy | Hospitality | 1978 |
| Siipo Estate Oy | Real estate | 2009 |
| Siipotec Oy | Manufacturing | 2022 |
| Siiran Turkis Oy | Agriculture & fishing | 2012 |
| Silta-asennus Mäkelä Oy | Construction | 2021 |
| Siltera Oy | Manufacturing | 1989 |
| SimpleVis Oy | Education | 2022 |
| Sistemo Oy | Real estate | 1992 |
| Sisustus Fors Oy | Construction | 2019 |
| Solar Kaihdin Oy | Wholesale & retail | 2004 |
| Solargrain Oy | Real estate | 2017 |
| SoraleX Oy | Construction | 2014 |
| SpectBros Oy | Wholesale & retail | 2025 |
| Stable Haapakangas Oy | Financial services | 1992 |
| Station Clothing Box Oy | Wholesale & retail | 1978 |
| Steelpert Finland Oy | Manufacturing | 2003 |
| SunBowling Oy | Arts & recreation | 2012 |
| SunOne Invest Oy | Wholesale & retail | 2018 |
| SunSugaring Ky | Wholesale & retail | 2013 |
| Suomen Keskusvaraamo Oy | Hospitality | 2014 |
| Supola Oy | Real estate | 1990 |
| Suunnittelu HVihelä Oy | Professional & scientific | 2017 |
| Suunnittelu Laitala Oy | Professional & scientific | 2017 |
| Sydänmetsä Oy | Construction | 2018 |
| Sähköalapalvelu Siermala Ky | Professional & scientific | 2015 |
| Sähköasennus A Kokko Oy | Construction | 1998 |
| Sähköasennus Jukka Tömisevä Oy | Construction | 2017 |
| Sähköliike Kalajoki Ky, Pauli Kippola ja Kaija Jaakola | Construction | 1976 |
| Sähköpalvelu-PRO Kalajoki Oy | Construction | 1997 |
| Sähkötarkastus Mikkonen Oy | Professional & scientific | 2004 |
| Särkkäin Mökkipalvelu Oy | Administrative & support | 2022 |
| Särkkäin Pihviravintola Oy | Hospitality | 2012 |
| Särkkäin Varikko Oy | Real estate | 2024 |
| Särkkäin varaosa Oy | Wholesale & retail | 2024 |
| T & A Mämmelä Oy | Professional & scientific | 1998 |
| T Nissinen Oy | Construction | 2012 |
| T. Kestilä Oy | Construction | 1993 |
| T. Kupari Oy | Construction | 2014 |
| T.A Tilikontrolli Oy | Real estate | 1991 |
| TKP Konetyö Oy | Construction | 2024 |
| TL-Puunkaato Oy | Agriculture & fishing | 2012 |
| TLB Holding Oy | Financial services | 2024 |
| TLB Invest Oy | Hospitality | 2022 |
| TNTimperi Oy | Construction | 2020 |
| TPH Consulting Oy | Construction | 2019 |
| TT Boat Oy | Manufacturing | 2021 |
| Tabasco Marin Ky | | 1983 |
| Taksi Jarmo Nevalainen Ky | Transport & logistics | 2006 |
| Taksipalvelu Toni Jämsä Ky | Transport & logistics | 2023 |
| Talenom Talouspalvelu Oy | Professional & scientific | 1986 |
| Tapani Haapakangas Ky | Transport & logistics | 1984 |
| Tapioland Oy | Arts & recreation | 1986 |
| Tapionkuusen Tupa Oy | Hospitality | 1979 |
| Tapzza Oy | Transport & logistics | 2014 |
| Tarcounts Oy | Professional & scientific | 2009 |
| Tarja Suni Oy | Health & social care | 1991 |
| Tarvikemotti Oy | Wholesale & retail | 1985 |
| Tasku Invest Oy | Real estate | 2015 |
| Tatsigym Oy | Arts & recreation | 2019 |
| Tavastit Oy | Transport & logistics | 1980 |
| Team Päivärinta Oy | Other services | 2024 |
| Tehokerroin Oy | Professional & scientific | 2023 |
| Tekninen Toimisto Tatu Mämmelä Oy | Real estate | 1983 |
| Teknis Oy | Real estate | 2024 |
| Tevi Systems Oy | Construction | 2017 |
| Thunder Road Oy | Professional & scientific | 2009 |
| Tili ja Isännöinti Jukola Oy | Professional & scientific | 2012 |
| Tili ja Laskenta Heikkinen Oy | Professional & scientific | 1993 |
| Tilintarkastus Hukka Oy | Professional & scientific | 2018 |
| Tilipalvelu Olkkola Oy | Professional & scientific | 1989 |
| TipTopTyö Oy | Construction | 2023 |
| Titan Events Oy | Administrative & support | 2024 |
| Titan Holding Oy | Financial services | 2025 |
| Tolpanmäki Oy | Administrative & support | 1996 |
| Topi-Keittiöt Oy | Manufacturing | 2015 |
| Trilogiline Oy | Wholesale & retail | 2007 |
| Tunnelman tuojat avoin yhtiö | Wholesale & retail | 2006 |
| Tuontitukku FI Oy | Wholesale & retail | 1996 |
| Tuottoplus Oy | Information & communication | 2018 |
| Turkis-Keisarit Oy | Agriculture & fishing | 1996 |
| Turkis-Liias Oy | Agriculture & fishing | 1995 |
| Turkisateljee Eija Ky | Manufacturing | 1984 |
| Turkistarha A Ylitalo Oy | Agriculture & fishing | 1993 |
| Turkistarha E. Manninen Oy | Agriculture & fishing | 1980 |
| Turkistarha Janne Manninen Oy | Agriculture & fishing | 2010 |
| Turkistarha Matti Apuli Oy | Agriculture & fishing | 2000 |
| Turner Group Oy | Professional & scientific | 1992 |
| Turner Ovipalvelu Oy | Wholesale & retail | 1990 |
| Turner Service Oy | Manufacturing | 2021 |