| Sähkö Tawastia Oy | Construction | 1996 |
| Sähkö- ja Automaatiosuunnittelutoimisto SAUT Oy | Professional & scientific | 1994 |
| Sähkö-Saanso Oy | Construction | 2019 |
| Sähköasennus Haapanen Oy | Construction | 2016 |
| Sähköasennus JP Vähätalo Oy | Construction | 2010 |
| Sähköasennus Lumen Oy | Construction | 2002 |
| Sähköasennus Mäkivirta Oy | Construction | 2019 |
| Sähköasennus Vesa Merjavuo OY | Construction | 2007 |
| Sähköasennus Viherä Oy | Construction | 2015 |
| Sähköpiste Rajala Ky | Construction | 1986 |
| Sähkötep Oy | Construction | 2009 |
| Sähkötyö Pasi Nuottakari Oy | Construction | 2023 |
| Säätö Energy Oy | Construction | 2022 |
| T&M Moniapu Oy | Construction | 2014 |
| T&T Vanhanen Oy | Information & communication | 2018 |
| T. Korkeamäki Ky | Professional & scientific | 1989 |
| T. Toukonen Oy | Wholesale & retail | 2019 |
| T. Vihmalaakso Oy | Transport & logistics | 1996 |
| TA Haapaniemi Oy | Wholesale & retail | 2021 |
| TB Invest Oy | Administrative & support | 2020 |
| TBS-Catering Oy | Hospitality | 2025 |
| TES Ecommerce Oy | Wholesale & retail | 2021 |
| TETRADENT Oy | Health & social care | 2000 |
| TH Balance Oy | Professional & scientific | 2014 |
| TH Ravintolat Oy | Hospitality | 1992 |
| TH-Rak Oy | Construction | 2021 |
| TJ-Stocks Oy | Construction | 1983 |
| TJ-Sähkö Oy | Construction | 1987 |
| TJH Saneeraus Oy | Construction | 2019 |
| TJT-rakennusyhtymä Ky | Construction | 1985 |
| TK-Box Oy | Real estate | 1991 |
| TL Collection Oy | Wholesale & retail | 2026 |
| TNM-Consulting Ky | Information & communication | 2002 |
| TO Events Oy | Arts & recreation | 2023 |
| TOM-Works Oy | Construction | 2006 |
| TP Toimitilat Oy | Real estate | 2023 |
| TR Audit Oy | Professional & scientific | 2021 |
| TRK Invest Oy | Construction | 2007 |
| TS Platinum Oy | Professional & scientific | 2018 |
| TS-Ins Oy | Professional & scientific | 2018 |
| TT-Installation Oy | Manufacturing | 2023 |
| TT-investment Oy | Real estate | 2009 |
| TTA ratkaisut Oy | Health & social care | 2025 |
| TTA-Capital Oy | Wholesale & retail | 2024 |
| TV-Sävel Oy | Wholesale & retail | 1985 |
| Taabeli Oy | Professional & scientific | 2015 |
| Tacit Oy | Professional & scientific | 2020 |
| Taide Tuulikki Viitala Oy | Arts & recreation | 2017 |
| Taimi-koulutus Oy | Professional & scientific | 2019 |
| Taitekohta Tiina Kuopanportti Oy | Education | 2019 |
| Taksia Oy | Transport & logistics | 2021 |
| Taksiliikenne Helander Oy | Transport & logistics | 2003 |
| Taksiliikenne Purhonen Oy | Transport & logistics | 2009 |
| Taksipalvelu J. Köngäs Oy | Transport & logistics | 2017 |
| Taksipalvelu Satellite Oy | Transport & logistics | 2010 |
| Taletuu Oy | Wholesale & retail | 2021 |
| Talo-Osakeyhtiö Hämeen Suoja | Real estate | 1930 |
| Talomme Oy | Construction | 2007 |
| Talorakennus Kokko Oy | Construction | 2015 |
| Talotawastia Oy | Professional & scientific | 2014 |
| Talotekniikka Hile Oy | Construction | 1978 |
| Taloushallinto Tabermann Oy | Professional & scientific | 2023 |
| Talousteema Oy | Information & communication | 1988 |
| Tammelan Sammutin Ky | Manufacturing | 1985 |
| Tammelan Tontti Oy | Real estate | 2004 |
| Tandife Oy | Financial services | 1989 |
| Tankkaus Group Oy | Wholesale & retail | 2025 |
| Tanssikoulu TR Studio Oy | Education | 2018 |
| Tatepaja Oy | Professional & scientific | 2022 |
| Tavastia Capital Oy | Real estate | 2018 |
| Tavastia Koulutus Oy | Education | 2015 |
| Tavastia Software Oy | Information & communication | 2019 |
| Tawast Bike Group Oy | Wholesale & retail | 2017 |
| Tawastia Bowling Oy | Wholesale & retail | 2000 |
| Tawastia Golf & Country Club Oy | Arts & recreation | 1988 |
| Tawastia House Oy | Construction | 1998 |
| Tawastia Invest Oy | Real estate | 1986 |
| Tawastia Optiikka Oy | Wholesale & retail | 2005 |
| Tawastia Rakennus Oy | Construction | 2007 |
| Tawastia Sora Oy | Mining & quarrying | 2008 |
| Tawastiatrans Oy | Transport & logistics | 2009 |
| Taxicar Finland Oy | Transport & logistics | 2001 |
| TeKar Oy | Other services | 2012 |
| TeVe -maalaus Oy | Construction | 2023 |
| Team2 Oy | Information & communication | 2013 |
| Techmi Oy | Construction | 2022 |
| Tecintecci Oy | Transport & logistics | 2023 |
| Tehojousto Oy | Professional & scientific | 2010 |
| Tehokas Ratkaisut Oy | Wholesale & retail | 2015 |
| Tehorax Oy | Construction | 2021 |
| Tekijäpalvelu Oy | Administrative & support | 2004 |
| Teknavi.com Oy | Wholesale & retail | 1992 |
| Teknillinen toimisto T. Oinonen Oy | Wholesale & retail | 1987 |
| Tele-Honkanen Oy | Construction | 1990 |
| Temeko Oy | Wholesale & retail | 1979 |
| Temeko-Invest Oy | Real estate | 1989 |
| Temperance Brewing Oy | Manufacturing | 2024 |
| Tempore Henkilöstöpalvelut Oy | Administrative & support | 2008 |
| Tenho Properties Oy | Real estate | 1992 |
| Tepamer Oy | Wholesale & retail | 2022 |