| Investor Services Ltd | Extraterritorial | 2025 |
| Invictus Diving & Marine Services Limited | Professional & scientific | 2014 |
| Invictus Project Services Ltd | Construction | 2019 |
| Invictus Sales Group Ltd | Professional & scientific | 2025 |
| Invinciflow UK Ltd | Construction | 2025 |
| Invisaid Limited | Information & communication | 2025 |
| Invisible Partners Limited | Professional & scientific | 2025 |
| Invisible Skate Tribe Ltd | Education | 2024 |
| Invisible Wind Factory Limited | Arts & recreation | 2014 |
| Invitebay Limited | Wholesale & retail | 2017 |
| Invrt Limited | Information & communication | 2025 |
| Inwood Inns Ltd | Hospitality | 2012 |
| IO Integration Limited | Information & communication | 2012 |
| Iodice Properties Ltd | Real estate | 2024 |
| IOI Trading Ltd | Wholesale & retail | 2023 |
| IOL Safety Support Ltd | Public administration | 2024 |
| Ioma Clothing Company Limited | Manufacturing | 1952 |
| Ioma Services Group Limited | Professional & scientific | 2019 |
| Ioma Sunshine Limited | Manufacturing | 2015 |
| ION Developments Limited | Extraterritorial | 2018 |
| ION Facilities Management Group Ltd | Administrative & support | 2021 |
| ION Group Ltd | Administrative & support | 2022 |
| ION Liverpool Partnership Limited | Extraterritorial | 2012 |
| ION Partnerships Limited | Real estate | 2017 |
| ION Projects Limited | Real estate | 2003 |
| ION Property Developments Limited | Real estate | 1998 |
| ION Property Group Limited | Financial services | 2016 |
| ION Regeneration Limited | Real estate | 2017 |
| ION Search Europe Ltd | Extraterritorial | 2015 |
| ION Steam Mill Limited | Real estate | 2015 |
| Ionalexandru Ltd | Construction | 2019 |
| Iontach Limited | Professional & scientific | 2012 |
| Ionut Gotu Ltd | Transport & logistics | 2025 |
| Ionut Sandu Ltd | Information & communication | 2024 |
| Ionutz Cleaning Services Ltd | Administrative & support | 2023 |
| Iordache Interior Construction Ltd | Construction | 2019 |
| Iospheresolutions Ltd | Information & communication | 2023 |
| IP Presents Limited | Information & communication | 2019 |
| Ip's Associates Limited | Professional & scientific | 2017 |
| Ip's Investment Limited | Real estate | 2014 |
| Ip-Office Northwest Limited | Information & communication | 2005 |
| IPA Holdings Ltd | Financial services | 2024 |
| Ipanda Tax Limited | Professional & scientific | 2024 |
| Ipave Driveways Ltd | Administrative & support | 2023 |
| IPB Compliance Ltd | Professional & scientific | 2014 |
| IPC Fire Protection Limited | Financial services | 2021 |
| Ipci NW Limited | Construction | 2019 |
| Ipct Ltd | Wholesale & retail | 2023 |
| IPG Construction (Central) Ltd | Construction | 2024 |
| IPG Construction (Portside) Ltd | Construction | 2024 |
| IPG Group Ltd | Construction | 2025 |
| IPG Investment Ltd | Financial services | 2025 |
| IPG Maintenance Ltd | Real estate | 2025 |
| IPG Oak Property Ltd | Real estate | 2021 |
| IPG Stanley Road Ltd | Real estate | 2022 |
| Ipifeni Ltd | Information & communication | 2021 |
| IPM Telecoms Ltd | Information & communication | 2019 |
| Iprogress Ltd | Information & communication | 2005 |
| IPS ( CAM ) Global Limited | Wholesale & retail | 2025 |
| IPS Finance Ltd | Financial services | 2017 |
| IPS National Ltd | Administrative & support | 2016 |
| IPS Progression Limited | Administrative & support | 2015 |
| IPS Umbrella Medical Limited | Administrative & support | 2009 |
| Iptf Railway Services Ltd | Construction | 2015 |
| IQ Music Limited | Arts & recreation | 1984 |
| IQ Structural Ltd | Professional & scientific | 2024 |
| IQ Ventures Limited | Construction | 2012 |
| IQ7 Enterprise Limited | Transport & logistics | 2018 |
| IQ707 Ecom Ltd | Wholesale & retail | 2023 |
| Iqbal Grocers Ltd | Wholesale & retail | 2018 |
| Iqra Islamic Empowerment Center CIC | Education | 2025 |
| Irada Ltd | Wholesale & retail | 2024 |
| Iranian Amigos Ltd | Hospitality | 2022 |
| IRB Property Investments Limited | Real estate | 2013 |
| IRB Transport Ltd | Transport & logistics | 2025 |
| IRB2012 Limited | Real estate | 2022 |
| IRC Construction Ltd | Construction | 2025 |
| Irebel Consulting & Services Ltd | Information & communication | 2023 |
| Ireland Road Homes Limited | Construction | 2018 |
| Ireland's Deli Limited | Hospitality | 2026 |
| Irenaeus Limited | Professional & scientific | 2003 |
| Irigait Ltd | Administrative & support | 2017 |
| Irina Luca Ltd | Transport & logistics | 2017 |
| Irina Shomron Limited | Professional & scientific | 2023 |
| Iris Properties Group Ltd | Real estate | 2023 |
| Iris Support Ltd | Health & social care | 2026 |
| Irish Community Care Ltd | Information & communication | 2010 |
| Irish Concert PUB Co Ltd | Hospitality | 2024 |
| Irish Ferries (U.K.) Limited | Transport & logistics | 1971 |
| Irish Ferries (U.K.) Services Limited | Transport & logistics | 2013 |
| Irish Temple PUB Co Ltd | Hospitality | 2024 |
| Irish Two Ltd | Hospitality | 2024 |
| IRK River I.T. Ltd | Information & communication | 2011 |
| Irkb.Me Ltd | Information & communication | 2023 |
| Irland Molyneux Limited | | 1963 |
| Irms Global Ltd | Information & communication | 2024 |
| Iroko Rock Properties Limited | Real estate | 2023 |
| Iron Beach Ventures Ltd | Information & communication | 2018 |
| Iron Fit Limited | Wholesale & retail | 2021 |
| Iron Shield Global Ltd | Other services | 2025 |