| Comars Ab | Lapväärtti | 2014 |
| Combiholding Oy | Lahnajärvi | 2015 |
| Commentarius Oy | Helsinki | 2015 |
| Common Ground Ltd Oy | Helsinki | 1990 |
| Community Center Jahaka Oy | Varkaus | 2002 |
| Community Centre Service Oy | Kirkkonummi | 2001 |
| Compandben SA Suomen sivuliike | Parainen | 2021 |
| Compass Consulting Oy | Pirkkala | 2023 |
| Compass Human Resources Group Finland Oy Ab | Helsinki | 1994 |
| Compass360 Oy | Ypäjä | 2026 |
| Compite Oy | Kantvik | 2011 |
| Composer Oy | Lahti | 2020 |
| Comprendum Oy | Dragsvik | 2017 |
| Compurent Oy | Kärrby | 1990 |
| Computo Oy | Tuomikylä | 2020 |
| CompyHome Services Oy | Espoo | 2025 |
| Coms Partners Oy | Lokalahti | 2017 |
| Comsan Oy | Otalampi | 2007 |
| Comscan Oy | Vantaa | 1985 |
| Comum Oy | Säynätsalo | 2018 |
| Con and tender Oy | Helsinki | 2024 |
| ConJa Oy | Espoo | 2018 |
| ConSan Oy | Helsinki | 2014 |
| Concentrix Finland Oy | Helsinki | 2002 |
| Concorde Travel Group Oy | Lappeenranta | 1992 |
| Condo Finland Oy | Osoite Tuntematon | 2016 |
| Conduco Pactum Oy | Haapaluoma | 2020 |
| ConeFreePet Oy | Helsinki | 2026 |
| Connection Finland Oy | Espoo | 2017 |
| Consilio Bono Oy | Nokia | 2018 |
| Consilio Nova Oy | Espoo | 2025 |
| Consultagency Saukko Oy Ab | Närpiö | 2020 |
| Consulting CH-MA Oy | Helsinki | 2021 |
| Consulting FFC Oy | Espoo | 1987 |
| Consulting Large Project Oy | Helsinki | 2021 |
| Consulting Wise Oy | Helsinki | 2020 |
| Consumer Retention Services Oy | Helsinki | 2022 |
| Contact & Travel Finland Oy | Vaasa | 2007 |
| Contact In Oy | Helsinki | 2013 |
| Contact-Center Masters Oy | Kirkkonummi | 2019 |
| Containertrade & Cargo Solutions Wasa Ltd Oy | Vaasa | 2021 |
| Continent Invest Oy | Nummela | 2017 |
| Contio Henkilöstöpalvelut Oy | Turku | 2019 |
| Contio PKS Rakentaminen Oy | Turku | 2021 |
| Contisar Oy | Lappeenranta | 2026 |
| Contmix Oy | Helsinki | 2008 |
| Control Kaupanturvavalvonta Oy | Raisio | 1996 |
| Control Rent Security Oy | Hämeenlinna | 2006 |
| Controlteam Nemous Oy | Mikkeli | 2016 |
| Conventures Finland Oy | Turku | 1983 |
| Convergint Finland Oy | Helsinki | 2025 |
| Conwise Rent Oy | Tuusula | 2024 |
| Cookie Capital Oy | Espoo | 2026 |
| CoolBlast Oy | Kankaanpää | 2017 |
| Coolcation Finland Oy | Espoo | 2024 |
| Coor Service Management Oy | Espoo | 1999 |
| Copterman Oy | Muurla | 2013 |
| Coptio Oy | Turku | 2001 |
| Copy Shop Oy | Espoo | 1990 |
| Copy T Oy | Linnantaus | 2009 |
| Core Staffing Oy | Jyväskylä | 2024 |
| CoreTalent Työvoima Oy | Lahti | 2026 |
| Corenum Oy | Turku | 2015 |
| Coreorient Oy | Helsinki | 2011 |
| Coreware Oy | Tampere | 2004 |
| CornerStone Siivous Palvelut Oy | Tammisaari | 2025 |
| Cortana Pizzeria avoin yhtiö | Helsinki | 2015 |
| Corvara osuuskunta | Helsinki | 2017 |
| Cosari oy | Salo | 2020 |
| Cosaunica Oy | Espoo | 2021 |
| Cosci-tuning Oy | Helsinki | 1997 |
| Cosmera Oy | Littoinen | 1991 |
| Cosmo Promotions Oy | Sundsberg | 1996 |
| Costa Clean Siivous palvelut Oy | Vantaa | 2023 |
| Costa Nord Oy | Helsinki | 2016 |
| Costacon Oy | Helsinki | 2006 |
| Coteens Oy | Kauniainen | 2010 |
| Cotse Oy | Porvoo | 1990 |
| Cottari Markkinointi Oy | Siuro | 2012 |
| Cottari Oy | Siuro | 2009 |
| Cottari Technologies Oy | Siuro | 2016 |
| Court Lake Oy | Tampere | 2020 |
| Couvet Oy | Oulu | 2025 |
| Covered Oy | Kuopio | 2024 |
| Cowabunga Oy | Mikkeli | 2023 |
| Coxa Oy | Tampere | 2001 |
| Craftman Oy | Oulu | 2011 |
| Craftwise Oy | Nokia | 2025 |
| Cramo Finland Oy | Vantaa | 2007 |
| Cramo Oy | Vantaa | 1954 |
| Crane Crew Oy | Jakari | 2020 |
| Crane Hill Invest Oy | Kuopio | 2015 |
| Crauser Oy | Espoo | 2017 |
| Crawford & Company Finland Oy | Helsinki | 2019 |
| Crea Group Oy | Helsinki | 2013 |
| CreaCap Oy | Helsinki | 2016 |
| Creagent Oy | Helsinki | 2016 |
| Crealo Group Oy | Ojakkala | 2015 |
| Creasell, Creative Selling Ky | Helsinki | 2005 |
| Credit Agency Finland Oy | Ii | 2013 |