| Interiors & Floor Design Limited | Wholesale & retail | 1992 |
| Interiors Inc. Limited | Wholesale & retail | 2010 |
| Interlight Limited | Professional & scientific | 2008 |
| Interline Electrical Wholesale Ltd | Wholesale & retail | 2001 |
| Interlink Health Consulting Ltd | Information & communication | 2026 |
| Intermark Medical (NI) Ltd | Manufacturing | 2020 |
| Intermediary Capital Investments Ltd | Administrative & support | 2020 |
| Intermediate Medical Solutions Ltd | Education | 2026 |
| International Beauty Salon Ltd | Other services | 2019 |
| International Construction Warranties Limited | Financial services | 2015 |
| International Electrical Safety Rules Organisation Ltd | Professional & scientific | 2025 |
| International Hair Salon Ltd | Other services | 2019 |
| International House Belfast Limited | Education | 2006 |
| International Synergies (Northern Ireland) Limited | Professional & scientific | 2014 |
| International Therapy Center Limited | Wholesale & retail | 2024 |
| Interpay UK Limited | Administrative & support | 2017 |
| Interpress (NI) Ltd | Manufacturing | 2004 |
| Intl Embryology Locums Ltd | Health & social care | 2014 |
| Into the Melting POT Limited | Wholesale & retail | 2017 |
| Intracontext Ltd | Professional & scientific | 2015 |
| Intragen Partners Limited | Professional & scientific | 2024 |
| Intrepid Toad Ltd | Information & communication | 2025 |
| Intrical Investments NI Ltd | Real estate | 2024 |
| Intrinsic AI Ltd | Information & communication | 2024 |
| Intrinsic Offshore Solutions Ltd | Professional & scientific | 2015 |
| Intrinsync Ltd | Information & communication | 2025 |
| Intuitive Eating Hub Ltd | Health & social care | 2023 |
| Intumodular Ltd | Hospitality | 2024 |
| Intupod Limited | Hospitality | 2015 |
| Inuvet UK Ltd | Manufacturing | 2023 |
| Inver Court Properties Limited | Households | 2004 |
| Inverary Wood Management Limited | Households | 2004 |
| Inverted Pole Academy Ltd | Arts & recreation | 2023 |
| Invest Hill Limited | Financial services | 2011 |
| Invest-Boat : Scraps, Rental & Shipping Ltd | Manufacturing | 2025 |
| Investment & Mortgage Centre Limited | Financial services | 2011 |
| Investment Opensource Ltd | Financial services | 2023 |
| Investnet Events Ltd | Administrative & support | 2025 |
| Investsec Group Limited | Real estate | 2019 |
| Invicktus Limited | Health & social care | 2021 |
| Invictus Automotive Ltd | Professional & scientific | 2026 |
| Invincible Marine & Offshore Supply Co Limited | Wholesale & retail | 2016 |
| Invisible Borders Ltd | Administrative & support | 2021 |
| Invisible Building Ltd | Information & communication | 2021 |
| Invitrocue UK Ltd | Extraterritorial | 2018 |
| Invoicefair Finance (NI) Limited | Financial services | 2020 |
| IO Web Limited | Administrative & support | 2014 |
| IOA Personal Lines Ltd | Financial services | 2018 |
| ION Technologies Limited | Information & communication | 1999 |
| Iona Star Capital Limited | Financial services | 2023 |
| Iona Star Nominees Limited | Financial services | 2024 |
| Ionad Uíbh Eachach | Health & social care | 2015 |
| Ionic Technologies (Belfast) Limited | Water & waste | 2026 |
| Ionoverse Ltd | Information & communication | 2025 |
| Ionsight Limited | Information & communication | 2025 |
| Iota Ventures Limited | Wholesale & retail | 2024 |
| Ipaypdq Limited | Information & communication | 2022 |
| Ipgni Synergy Limited | Construction | 2023 |
| Iphix (2021) Ltd | Other services | 2020 |
| Iphix Belfast Limited | Information & communication | 2015 |
| Iphix Phones Wholesale Ltd | Wholesale & retail | 2015 |
| Iphix Tech NI Ltd | Other services | 2023 |
| Ipls Exam Tuition Ltd | Education | 2023 |
| IPN Communications Limited | Information & communication | 2010 |
| Ippnetwork Ltd | Information & communication | 2023 |
| IPR Guru Ltd | Information & communication | 2026 |
| Iprint and Design Enterprises Limited | Manufacturing | 2015 |
| IPS (2024) Ltd | Hospitality | 2024 |
| Ipsolutionsni Limited | Information & communication | 2013 |
| IQ Ultima Ltd | Wholesale & retail | 2025 |
| Ireel Group Limited | Information & communication | 2025 |
| Ireland Safety Training Ltd | Wholesale & retail | 2025 |
| Ireland SE CIC | Education | 2012 |
| Ireland Tours Limited | Transport & logistics | 2016 |
| Irene International Limited | Manufacturing | 2024 |
| Irene Leahey Agencies Ltd | Wholesale & retail | 2012 |
| Ireton Ltd | Hospitality | 2016 |
| Irfu Charitable Trust (Northern Ireland) | Health & social care | 2007 |
| Iris Sanderson Ltd | Wholesale & retail | 2023 |
| Irish Biomethane (NI) Ltd | Professional & scientific | 2024 |
| Irish Cargo and Clearance Ltd | Transport & logistics | 2025 |
| Irish Curry Awards (2022) Ltd | Professional & scientific | 2021 |
| Irish Curry Awards Ltd | Hospitality | 2016 |
| Irish Entertainment Group Ltd | Arts & recreation | 2025 |
| Irish FA Foundation Limited | Arts & recreation | 2016 |
| Irish Food Companies Ltd | Manufacturing | 2021 |
| Irish Football Association Limited | Arts & recreation | 1909 |
| Irish Gods Ltd | Manufacturing | 2023 |
| Irish Gothic Ltd | Information & communication | 2017 |
| Irish Grouse Conservation Trust - the | Arts & recreation | 2006 |
| Irish Hill Wind Ltd | Energy | 2016 |
| Irish Logistics Ltd | Transport & logistics | 2019 |
| Irish Long Distance Riding Association Limited | Arts & recreation | 1996 |
| Irish Media Solutions Limited | Administrative & support | 2025 |
| Irish Music Ireland Limited | Information & communication | 2012 |
| Irish News Limited - the | Information & communication | 1986 |
| Irish Pages Limited | Information & communication | 2003 |
| Irish Selection Limited | Hospitality | 2010 |
| Irish Stadium Communities Association Trading AS Isca Limited | Other services | 2013 |
| Irish Temperance League (Incorporated 1900). | Other services | 1900 |