| Jämsän Tilikonsultointi Oy | Professional & scientific | 2008 |
| Jämsän Toimistovaruste Oy | Wholesale & retail | 2007 |
| Jämsän Varaosamyynti Ky | Wholesale & retail | 2003 |
| Jämsän Vesu Ky | Construction | 1994 |
| Jämsän Ykkösvaraosa Oy | Wholesale & retail | 2007 |
| Jämsän Yrityskiinteistöt Oy | Real estate | 2003 |
| Jämsän kebab pizzeria avoin yhtiö | Hospitality | 2013 |
| Jämsänjokilaakson Jäähalli Oy | Arts & recreation | 1993 |
| Järvelä & Ståhlberg Yhtiöt Oy | Construction | 1975 |
| Järvinen Invest Oy | Construction | 2007 |
| K&M Investments Oy | Real estate | 2021 |
| KAKE Finland OY | Construction | 2014 |
| Kisa Taksi OY | Transport & logistics | 2020 |
| KJM Sportfishing Oy | Administrative & support | 2021 |
| KL Log Ky | Professional & scientific | 2014 |
| Kondoja Metsäpalvelu OY | Agriculture & fishing | 2011 |
| KSR Palvelut Oy | Manufacturing | 2025 |
| KT-KaSari Oy | Administrative & support | 2017 |
| KTR-Konepalvelu Oy | Administrative & support | 2010 |
| KaPe Holding Oy | Administrative & support | 2023 |
| Kakaristo Oy | Professional & scientific | 2005 |
| Kallioranta Investment Oy | Financial services | 2013 |
| Kanttikuljetus Oy | Transport & logistics | 2020 |
| Karboni Oy | Arts & recreation | 2003 |
| Kari Viidanoja Ky | Wholesale & retail | 1993 |
| Kasami-Jämsä Oy | Real estate | 2017 |
| Kaukon Oy Jämsä | Wholesale & retail | 1952 |
| Kauneuskeskus Pirjo Oy | Other services | 2008 |
| Kaza-Holding Ltd Oy | Real estate | 1995 |
| KeS-Siltaykköset Oy | Professional & scientific | 2008 |
| Keijon Kenkä Oy | Wholesale & retail | 1989 |
| Kengityspalvelu Häyhänen Oy | Agriculture & fishing | 2012 |
| Keski-Suomen Polttoainepalvelu Oy | Wholesale & retail | 2024 |
| Keskusvoitelu Ky Seppo Virtanen | Manufacturing | 1990 |
| Ki Oy PB Group | Real estate | 2015 |
| Kiesiläinen & Tenhunen | Wholesale & retail | 2019 |
| Kiinteistö Oy Harvest Moon | Real estate | 2016 |
| Kiinteistö Oy Himoksen Aurinkopaikka | Real estate | 2009 |
| Kiinteistö Oy Himoksen Koivulanranta | Real estate | 1998 |
| Kiinteistö Oy Himoksen Kotkanpää | Real estate | 2021 |
| Kiinteistö Oy Himoksen Vallaton | Real estate | 2021 |
| Kiinteistö Oy Jämsän Olavinlinna | Real estate | 1991 |
| Kiinteistö Oy Jämsän Ratapuisto | Real estate | 1987 |
| Kiinteistö Oy Jämsänkosken Paulaharju | Real estate | 1996 |
| Kiinteistö Oy Jämsänmäki | Real estate | 1978 |
| Kiinteistö Oy Kivistönkatu 31-33 | Real estate | 2003 |
| Kiinteistö Oy Kivistöntie 9 Himos | Real estate | 2000 |
| Kiinteistö Oy Kähönen | Real estate | 1986 |
| Kiinteistö Oy Lukkoilantie 41 | Real estate | 2001 |
| Kiinteistö Oy Puutarha-Auvila | Real estate | 2021 |
| Kiinteistö Oy Päijänteen Helmi | Hospitality | 2007 |
| Kiinteistö Oy Sähköverstas | Real estate | 2015 |
| Kiinteistö Oy Vitikkalan Kartano | Real estate | 2000 |
| Kiinteistöhuolto J. Hagren Oy | Administrative & support | 2021 |
| Kiinteistönvälitys Tanja Heinonen Oy LKV | Real estate | 2017 |
| Kiinteistöyhtiö Almatop Oy | Real estate | 2006 |
| Kirvesmiespalvelu Mäntylä Oy | Construction | 2017 |
| Ko-Hu K & H Oy | Transport & logistics | 2011 |
| Kolo Foods Oy | Wholesale & retail | 2002 |
| Konetyö Huhtinen Oy | Administrative & support | 2023 |
| Koneviikarit Oy | Construction | 2016 |
| Korjaamo Kaurahuhti Ky | Manufacturing | 1982 |
| Kotiaho Kiinteistöt Oy | Real estate | 2020 |
| Krapina Oy | Hospitality | 1996 |
| Kuleshmann Oy | Hospitality | 2008 |
| Kuljetus Pohjonen Oy | Transport & logistics | 2016 |
| Kuljetus-Heinäjärvi Ky | Transport & logistics | 1993 |
| Kuljetusliike Erkki Ojala Oy | Transport & logistics | 1986 |
| Kuljetusliike Mauri Junnola Oy | Transport & logistics | 1995 |
| Kuljetusliike Naarajärvi Oy | Transport & logistics | 1980 |
| Kuljetusliike Raimo Pohjonen Oy | Transport & logistics | 1985 |
| Kuljetuspalvelu Kärki Oy | Transport & logistics | 2021 |
| Kulta-Jyrgen Oy | Wholesale & retail | 1990 |
| Kuntopari Oy | Wholesale & retail | 1987 |
| Kuruman Oy | Real estate | 1995 |
| LJ-Huolto Oy | Other services | 2010 |
| LVI-KAT Oy | Construction | 2006 |
| Laatoitus- ja rakennustyö Salmio Oy | Construction | 2025 |
| Lactos International Oy | Wholesale & retail | 2003 |
| Lainekallio Oy | Mining & quarrying | 2014 |
| LakiMari Lakipalvelut Oy | Other services | 2016 |
| Lamcon Oy | Construction | 2010 |
| Laukaan autopelti Kommandiittiyhtiö | Other services | 1986 |
| Leiskua Oy | Professional & scientific | 2019 |
| Lentomestari Oy | Education | 2024 |
| Lindroosin Sora Oy | Construction | 1979 |
| Lokola Oy | Wholesale & retail | 2002 |
| Lomahimos Oy | Real estate | 1987 |
| Lomanet Finland Oy | Hospitality | 2026 |
| Lopeisto Oy | Real estate | 2021 |
| Lumi Ventures Oy | Wholesale & retail | 2002 |
| LuoKor Oy | Wholesale & retail | 2020 |
| LuottoHoiva Oy | Health & social care | 2026 |
| Lvi Ramo Oy | Construction | 2025 |
| MEDI Connection Oy | Professional & scientific | 2012 |
| Mijapi OY | Other services | 2019 |
| MIP-Cargo Oy | Transport & logistics | 2025 |
| MIPA Consulting Oy | Construction | 2014 |
| MJ Rauta Oy | Wholesale & retail | 2021 |
| MMC-Consulting Oy | Professional & scientific | 2018 |