| Home Door Properties Limited | Construction | 2003 |
| Home-Start Lakeland | Health & social care | 2014 |
| Honne Technologies Ltd | Information & communication | 2023 |
| Hoofdoc Limited | Agriculture & fishing | 2023 |
| Hope U Crawl Limited | Wholesale & retail | 2025 |
| Hot WOK (Ensk) Limited | Hospitality | 2022 |
| Howard Power & Construction Ltd | Professional & scientific | 2017 |
| Howden Tools and Garage Equipment (UK) Ltd | Wholesale & retail | 2015 |
| HP Hire Limited | Administrative & support | 1999 |
| HR Richmond Properties Ltd | Construction | 2005 |
| HRD Solar Ltd | Construction | 2026 |
| Huey Limited | Wholesale & retail | 2016 |
| Hughes Building Contractors Ltd | Construction | 2008 |
| Hunters Moon Management Co Ltd | Households | 2004 |
| Hutchinson Clarke Ltd | Administrative & support | 2018 |
| Hydroponics Ireland Ltd | Wholesale & retail | 2025 |
| Hype & Holler Limited | Information & communication | 2014 |
| IBP (Enniskillen) Limited | Professional & scientific | 2017 |
| ICF Services Limited | Construction | 2015 |
| Icy-Sharp Ltd | Information & communication | 2024 |
| Identity Hairdressers Ltd | Other services | 2020 |
| IGS Medical Services Limited | Other services | 2019 |
| IH Engineering (NI) Ltd | Construction | 2023 |
| IJ International Ltd | Wholesale & retail | 2021 |
| Imperial Hotel (Enniskillen) Limited-The | Real estate | 1956 |
| IMS Corporate Services Limited | Financial services | 2016 |
| IMS Support Limited | Financial services | 2015 |
| Inan House Ltd | Professional & scientific | 2026 |
| Industraclean Ltd | Administrative & support | 2023 |
| Industria Company (Ulster) Limited | Real estate | 1965 |
| Industrial Business Properties Ltd | Real estate | 2014 |
| Industrialspraymasters Limited | Other services | 2025 |
| Infinity Effects Holdings (Ireland) Ltd | Financial services | 2024 |
| Infinity Innovative Coatings Ltd | Manufacturing | 2019 |
| Inishmacsaint Investco Ltd | Real estate | 2016 |
| Inishmore Island B&B Ltd | Hospitality | 2023 |
| Inishmore Marine Ltd | Other services | 2021 |
| Inishmore Venison Limited | Agriculture & fishing | 2019 |
| Inishrush Properties Limited | Real estate | 2007 |
| Inishshore Limited | Wholesale & retail | 2016 |
| Inn Stock Services (NI) Limited | Professional & scientific | 2013 |
| Innovation Brothers (Holdings) Limited | Financial services | 2023 |
| Innovation Brothers (NI) Limited | Wholesale & retail | 2023 |
| Inspird Design Ltd | Professional & scientific | 2024 |
| Inspire Architectural Design Ltd | Extraterritorial | 2006 |
| Insulate Ireland Limited | Construction | 2009 |
| Insurance Management Solutions Group Limited | Financial services | 2016 |
| Integral Applications Ltd | Information & communication | 2020 |
| Integral Customs Ltd | Administrative & support | 2021 |
| Interlux Systems Ltd | Construction | 2019 |
| Inventive Industries Ltd | Professional & scientific | 2023 |
| Inverbeira UK Limited | Financial services | 2018 |
| Ipolx Consulting Limited | Professional & scientific | 2012 |
| Irish Central Border Area Network Limited | Professional & scientific | 2001 |
| Irish Concert & Entertainment Protection Limited | Administrative & support | 2025 |
| Irish Evangelistic Band | Other services | 2020 |
| Irish Hemp Briquettes Ltd | Manufacturing | 2018 |
| Irish Pro Golf Tours Limited | Administrative & support | 2022 |
| Irvine's Farm Supplies Ltd | Wholesale & retail | 2026 |
| Irwin Consulting Services Ltd | Professional & scientific | 2021 |
| Irwin D Enterprises Ltd | Wholesale & retail | 2026 |
| Isle of Erne Ltd | Real estate | 2025 |
| Ispiri Holdings Limited | Wholesale & retail | 2012 |
| Ispiri Properties Limited | Real estate | 2012 |
| Ispiri Wheels (UK) Ltd | Wholesale & retail | 2005 |
| Ispiri Wheels Ltd | Wholesale & retail | 2014 |
| ITS Plant-Tech Ltd | Professional & scientific | 2008 |
| ITS Raining Tacos Limited | Hospitality | 2026 |
| ITS Wind Services Ltd | Manufacturing | 2024 |
| Ivan KEE Limited | Real estate | 1992 |
| IW Agri Ltd | Agriculture & fishing | 2026 |
| IW Automotive Ltd | Wholesale & retail | 2012 |
| J & J Developments Co. Ltd | Construction | 2003 |
| J Cathcart Limited | Wholesale & retail | 2023 |
| J Corr Contracts Ltd | Agriculture & fishing | 2023 |
| J Mcclean Ltd | Wholesale & retail | 2026 |
| J. & W. Cooper Developments Ltd | Professional & scientific | 1990 |
| J.M.C Electrical Engineering Limited | Construction | 2007 |
| J.O Management Ltd | Administrative & support | 2022 |
| Jaba Properties Limited | Real estate | 2005 |
| Jacopa-Deane Group Ltd | Water & waste | 2020 |
| Jaek Properties Ltd | Real estate | 2012 |
| Jaguar Polymers Limited | Manufacturing | 2018 |
| Jaikat Technologies Ltd | Construction | 2022 |
| Jalear Ltd | Real estate | 2024 |
| JAM Agri Ltd | Wholesale & retail | 2021 |
| Jamm Restaurants Ltd | Hospitality | 2011 |
| Jant Planning NI Ltd | Professional & scientific | 2020 |
| Japs (NI) Limited | Real estate | 2009 |
| Jara Estates Limited | Real estate | 2016 |
| Jardine Associates Limited | Professional & scientific | 2020 |
| Jason Clarke Transport Ltd | Transport & logistics | 2022 |
| JB Agri Ltd | Agriculture & fishing | 2024 |
| JB Custom Artwork Ltd | Arts & recreation | 2025 |
| JB Lets Ltd | Real estate | 2022 |
| JB Properties and Rentals Ltd | Real estate | 2024 |
| Jbni Trading Co Ltd | Wholesale & retail | 2025 |
| JCR Hire Ltd | Administrative & support | 2010 |
| JD Cafe and Catering Ltd | Hospitality | 2022 |
| JDB Supply’S Ltd | Wholesale & retail | 2025 |