| Ilmatar Merijärvi Oy | Energy | 2022 |
| Ilmatar Merikarvia Oy | Energy | 2022 |
| Ilmatar Offshore Ab | Energy | 2022 |
| Ilmatar Onshore Development Oy | Energy | 2023 |
| Ilmatar Ooperi Oy | Energy | 2022 |
| Ilmatar Paltamo Oy | Energy | 2021 |
| Ilmatar Pielavesi Oy | Energy | 2021 |
| Ilmatar Pielavesi Vornankorpi Oy | Energy | 2022 |
| Ilmatar Pihlajasuo Oy | Energy | 2022 |
| Ilmatar Saarijärvi Oy | Energy | 2022 |
| Ilmatar Seinäjoki Häjyjoki Oy | Energy | 2022 |
| Ilmatar Seinäjoki Oy | Energy | 2021 |
| Ilmatar Sievi Oy | Energy | 2022 |
| Ilmatar Solar Alajärvi Oy | Energy | 2022 |
| Ilmatar Solar Development Oy | Energy | 2019 |
| Ilmatar Solar Finland Oy | Energy | 2022 |
| Ilmatar Solar Haverinsuo Oy | Energy | 2023 |
| Ilmatar Solar HoldCo 1 Oy | Energy | 2023 |
| Ilmatar Solar Huutokoski Oy | Energy | 2023 |
| Ilmatar Solar Joroinen Oy | Energy | 2022 |
| Ilmatar Solar Murtolampi Oy | Energy | 2023 |
| Ilmatar Solar Pöytäsaarensuo Oy | Energy | 2023 |
| Ilmatar Solar Uusiniitty Oy | Energy | 2023 |
| Ilmatar Solar Verhonkulma Oy | Energy | 2024 |
| Ilmatar Solar Vuotsinsuo Oy | Energy | 2023 |
| Ilmatar Solar Ypyrinneva Oy | Energy | 2023 |
| Ilmatar Somero Oy | Energy | 2011 |
| Ilmatar Sonkajärvi Oy | Energy | 2021 |
| Ilmatar Stormskär & Väderskär Ab | Energy | 2023 |
| Ilmatar Uusikaarlepyy Oy | Energy | 2022 |
| Ilmatar Vermassalo Oy | Energy | 2022 |
| Ilmatar Virrat Oy | Energy | 2021 |
| Ilmatar Vågskär Ab | Energy | 2023 |
| Ilme Helsinki Oy | Manufacturing | 2020 |
| Ilme Oy Viittomakielialan tulkkaus- ja asiantuntijapalvelut | Professional & scientific | 2017 |
| Ilmelä Ikikesä Oy | Wholesale & retail | 2002 |
| Ilmestyskirjanpitäjä.Nyt! Ky | Professional & scientific | 2002 |
| Ilmiö Consulting Oy | Administrative & support | 2025 |
| Ilmiömäinen Agentuuri Oy | Professional & scientific | 2022 |
| Ilmoniemi Consulting Oy | Information & communication | 2021 |
| Ilo Perio Oy | Health & social care | 2020 |
| Ilo Wines Oy | Wholesale & retail | 2024 |
| Ilo-korut Oy | Manufacturing | 2013 |
| IloGym Oy | Arts & recreation | 2025 |
| Iloa Family Oy | Manufacturing | 2020 |
| Iloaelämään Sanna Soini Oy | Other services | 2018 |
| Ilobitti Oy | Professional & scientific | 2013 |
| Iloinen Planeetta Oy | Professional & scientific | 2022 |
| Iloinen tähti Osk | Administrative & support | 2015 |
| Iloiset Ateriat Oy | Hospitality | 2020 |
| Iloiset Kaverit Oy | Wholesale & retail | 2024 |
| Ilometri Oy | Arts & recreation | 1989 |
| Ilomäentien Juniorinurmi Oy | Arts & recreation | 2011 |
| Ilon Hetket Oy | Other services | 1976 |
| Ilona Group Oy | Wholesale & retail | 2016 |
| Ilona IT Oy | Wholesale & retail | 2010 |
| Ilona Pelli Oy | Professional & scientific | 1995 |
| Ilona Rauhala Oy | Health & social care | 2007 |
| Ilona Rista Oy | Arts & recreation | 2017 |
| Ilona Valmennus Oy | Professional & scientific | 2012 |
| Ilona Ventures Oy | Information & communication | 2026 |
| Ilona Works Finland Oy | Professional & scientific | 2014 |
| Ilonen & Co LKV Oy Ab | Real estate | 2025 |
| Ilonion Care Oy | Professional & scientific | 2018 |
| Iloresta Oy | Hospitality | 2018 |
| Iloria Oy | Wholesale & retail | 1993 |
| Ilot Oy | Wholesale & retail | 2021 |
| Ilove Creative Oy | Professional & scientific | 2011 |
| Ilpon Autohuolto Oy | Other services | 2026 |
| Ilpon autokorjaamo Oy | Other services | 2023 |
| Ilser Oy | Construction | 2022 |
| Ilu Holding Oy | Financial services | 2021 |
| Ilu Trust Oy | Financial services | 2025 |
| Ilusound Oy | Arts & recreation | 1990 |
| Iluusio Oy | Information & communication | 2023 |
| Ilva Green Solutions Oy | Wholesale & retail | 2024 |
| Ilves-Interiööri Oy | Wholesale & retail | 2005 |
| Imagate Oy | Financial services | 2007 |
| Image Hair & Beauty Oy | Other services | 2011 |
| Image Jewelry Avoin Yhtiö | Manufacturing | 1998 |
| Image Soft Oy | Information & communication | 1990 |
| Image-Point Oy | Wholesale & retail | 1995 |
| Imagedesk Finland Oy | Information & communication | 2018 |
| Imagemaker Creative Oy | Administrative & support | 2010 |
| Imagemaker Oy | Administrative & support | 1988 |
| Imagenary Oy | Professional & scientific | 2011 |
| Imagi Oy | Professional & scientific | 2020 |
| Imagian Observer Oy | Professional & scientific | 2012 |
| Imagian Oy | Professional & scientific | 2007 |
| Imaginatrix Oy | Information & communication | 2025 |
| Imagine Solutions Oy | Information & communication | 2025 |
| Imaginor Oy | Professional & scientific | 2020 |
| Imagokuva avoin yhtiö | Professional & scientific | 2005 |
| Iman ja Leena oy | Other services | 2021 |
| Imar Oy | Financial services | 1989 |
| Imascon Oy | Transport & logistics | 2008 |
| Imatran Silmäasema Mansikka Oy | Wholesale & retail | 1992 |
| Imax Autokorjaamo ja Pesula Oy | Other services | 2021 |
| Imbibe International Oy | Wholesale & retail | 2017 |
| Imboys Oy | Wholesale & retail | 2015 |