| Stone Charging Solutions Oy | Manufacturing | 2025 |
| Storsto Tjänst & Service Öppet bolag | Construction | 2015 |
| Storvall Management Ab Oy | Professional & scientific | 2025 |
| Straight Inspection Ab | Professional & scientific | 2025 |
| Strengbergs Habit Factory Ab Oy | Manufacturing | 2023 |
| Strengfors Capital Oy Ab | Financial services | 2021 |
| Studio Archigraph OY | Professional & scientific | 1992 |
| Studio Gros öppet bolag | Professional & scientific | 2011 |
| Studio PAP Ab | Professional & scientific | 1990 |
| Summerstreet Oy | Wholesale & retail | 2023 |
| SunFit Oy Ab | Arts & recreation | 2012 |
| Sunday Music Media Ab | Information & communication | 1990 |
| Sundelin International öppet bolag | Wholesale & retail | 2005 |
| Sundelins Pro Ab Oy | Administrative & support | 2025 |
| Sundero Oy | Information & communication | 2025 |
| Sunds Trädgård Ab | Agriculture & fishing | 1994 |
| Sundström Naprapatterapi Ab | Health & social care | 1987 |
| Suomen Ratahuolto Oy | Administrative & support | 2011 |
| Suomen Tarjoustoimisto Oy | Information & communication | 2024 |
| Suomen Ulkotulet Oy | Financial services | 1996 |
| Super Auto Blomström Oy | Other services | 2009 |
| Susanns Debet & Credit kb | Professional & scientific | 2001 |
| Svedje Oy | Energy | 2025 |
| Syla Fastigheter Ab | Real estate | 2020 |
| Synergy Scandic Oy | Wholesale & retail | 2014 |
| Syöte Skidessen, öppet bolag | Real estate | 1989 |
| Sähköhuolto Fränti Oy | Construction | 2025 |
| Sähköpalvelu Walberg Ab Oy | Construction | 2009 |
| Sämskar - Eisvikens Vattenandelslag | Water & waste | 2007 |
| Södergård Tom Ab | Agriculture & fishing | 2006 |
| Södös Entreprenad, öppet bolag | Transport & logistics | 1996 |
| T. Kellari Ky | Agriculture & fishing | 1979 |
| T.A Performance Oy | Other services | 2021 |
| T.J Östman Oy | Other services | 2016 |
| TA All-Service öppet bolag | Administrative & support | 2012 |
| TACK Service Oy Ltd | Professional & scientific | 2015 |
| TAXI Simon Jakobstad Ab | Transport & logistics | 2026 |
| TBT Multitjänst Ab Oy | Other services | 2022 |
| TH Property Investors Oy | Real estate | 2008 |
| THK Fastighet Ab | Real estate | 2007 |
| TICA Consulting Oy | Professional & scientific | 2008 |
| TJC-Support Öppet Bolag | Professional & scientific | 2013 |
| TKM invest Ab | Financial services | 2021 |
| TNMB-Holding Oy | Professional & scientific | 2024 |
| TPB Nordics Oy Ab | Manufacturing | 2024 |
| TPR Service Ab | Construction | 2004 |
| TR Automation Engineering Oy | Professional & scientific | 2006 |
| TR2 Invest AB | Real estate | 2025 |
| TRIA-Bygg Ab Oy | Construction | 2020 |
| TRM Service Ab | Construction | 2009 |
| TS Audit Ab | Professional & scientific | 2014 |
| TS-Huhtala Oy | Construction | 2017 |
| TS-Team Ab | Construction | 2016 |
| TSR Install Ab | Construction | 2018 |
| Taitoavain Oy | Professional & scientific | 2021 |
| Tallbiten Ab Oy | Wholesale & retail | 2018 |
| Tallmo Invest Ab | Administrative & support | 2022 |
| Tandklinik-Hammasklinikka Anders Virtanen Ab Oy | Health & social care | 2012 |
| Tandtekniskt laboratorium Jakodent Ab | Manufacturing | 2003 |
| Tanssiorkesteri Walkarit avoin yhtiö | Arts & recreation | 2009 |
| Taxi E Jansson Ab | Transport & logistics | 2026 |
| Te-Ro Oy | Construction | 2009 |
| Team Granqvist öppet bolag | Construction | 2018 |
| Team K Trail Ab | Arts & recreation | 2019 |
| Tec Heat Ab Oy | Construction | 2007 |
| Teklatalojen Lämpöhuolto Oy | Administrative & support | 2024 |
| Teri-Sali Ab | Arts & recreation | 2016 |
| Tervapaja Oy | Real estate | 2006 |
| The Anchorage Jakobstad Oy | Real estate | 2025 |
| Thomas Enroth Ab | Arts & recreation | 2023 |
| Thriambos Ab Oy | Financial services | 2018 |
| Tiibaa Media Ab Oy | Professional & scientific | 2016 |
| Today&Ever Oy | Health & social care | 2023 |
| Top D Ltd Oy | Wholesale & retail | 2016 |
| Torsvikens Hästcenter Ab - Torsvikenin Hevoskeskus Oy | Professional & scientific | 1986 |
| Toscana trattoria Ab | Hospitality | 2024 |
| Trackflow Ab Oy | Professional & scientific | 2022 |
| Trafikskola T Tuomi Ab | Education | 1973 |
| Transport Ab Granqvist | Transport & logistics | 2012 |
| Transport Johan Holmstedt Kb | Transport & logistics | 1983 |
| Transport Petterson Ab | Transport & logistics | 2002 |
| Truckshop Häggblom Ab Oy | Other services | 2016 |
| Två Gårdar öppet bolag | Wholesale & retail | 2017 |
| Twinsnk Oy | Professional & scientific | 2025 |
| Tyg & Tråd Ab Jakobstad | Wholesale & retail | 2014 |
| TähtiRisuaita Oy | Information & communication | 2023 |
| U&B Future Ab | Financial services | 2021 |
| Ullmys Oy Ab | Manufacturing | 2024 |
| Uniikkimatkat Oy | Administrative & support | 2014 |
| Utra Invest Ab | | 2026 |
| VBN Invest AB | Real estate | 2019 |
| VVN-Urakointi Oy | Construction | 2017 |
| Vallanin Vesi Oy Ab | Professional & scientific | 2014 |
| Vallgrav AB | Manufacturing | 2022 |
| Vallgren Ab | Construction | 2025 |
| Vanadis Fuels Ab Oy | Professional & scientific | 2022 |
| Varaosa Mara Oy Ab | Wholesale & retail | 2017 |
| Varea Invest Ab | Real estate | 2026 |
| Vasa gräv och transport Ab | Construction | 1992 |
| Vattenandelslaget Aqua | Water & waste | 2004 |