| Irish Tunnelling Ltd | Construction | 2006 |
| Irish Wagyu Ltd | Agriculture & fishing | 2014 |
| Irish Whiskey Guild CIC | Administrative & support | 2020 |
| Irish Wind and Marine Services Limited | Professional & scientific | 2020 |
| Iron & Timber Ltd | Administrative & support | 2025 |
| Ironborn Real Estate Limited | Wholesale & retail | 2023 |
| Irwin & Stewart Contracts Limited | Construction | 2018 |
| Irwin Acoustics Limited | Professional & scientific | 2019 |
| Isambard Associates Ltd | Administrative & support | 2015 |
| Isocom Transit L.P. | | 2015 |
| Isomark Invest L.P. | | 2017 |
| Isotech Ltd | Administrative & support | 2017 |
| ISX4 Resource Solutions Ltd | Administrative & support | 2026 |
| IT Barr Limited | Information & communication | 2014 |
| IT Synergies Limited | Information & communication | 2025 |
| It's LIT Tanning Ltd | Other services | 2019 |
| It’S a Car Thing Auto Sales Limited | Wholesale & retail | 2021 |
| Iur-Fm Limited | Wholesale & retail | 2010 |
| Iveagh Heating Limited | Construction | 2021 |
| Ivernia Holdings Ltd | Construction | 2025 |
| IVY Way Company Limited | Construction | 2022 |
| Iwox France Ltd | Wholesale & retail | 2013 |
| Ixisys Ltd | Information & communication | 2009 |
| Izzyboo Catering Limited | Hospitality | 2024 |
| J & C Crawley Building Contractors Limited | | 2005 |
| J & C Joinery Contracts Ltd | Construction | 2016 |
| J & J Retail Limited | Wholesale & retail | 2013 |
| J & L Machinery Ltd | Wholesale & retail | 2018 |
| J & M Lenagh Limited | Transport & logistics | 2016 |
| J & T Properties Limited | Real estate | 2005 |
| J a Cattle Ltd | Agriculture & fishing | 2020 |
| J and D Mechanical Services Ltd | Construction | 2022 |
| J and N Joinery Ltd | Construction | 2009 |
| J Canning Consulting Ltd | Construction | 2024 |
| J Convery Contracts Ltd | Construction | 2021 |
| J D L Contracts Ltd | Construction | 2007 |
| J Dawson Contracts Ltd | Administrative & support | 2024 |
| J E P Retail Ltd | Wholesale & retail | 2024 |
| J Harkin Ltd | Real estate | 2024 |
| J Hughes Medical Limited | Health & social care | 2011 |
| J Irwin Car Sales Ltd | Wholesale & retail | 2015 |
| J L O'Hagan & Co. Limited | Professional & scientific | 2006 |
| J Mccreesh Farming Limited | Agriculture & fishing | 2020 |
| J O'Hare Electrical Ltd | Construction | 2025 |
| J P Homes Limited | Construction | 1998 |
| J P Morgan Contracting Limited | Transport & logistics | 2019 |
| J R Waddell & SON Limited | Construction | 2004 |
| J Rice Building and Renovation Ltd | Construction | 2023 |
| J&J Cars Ltd | Wholesale & retail | 2020 |
| J&J Mckibbin Ltd | Construction | 2016 |
| J&J Morgan Ltd | Wholesale & retail | 2022 |
| J&J68 Ltd | Hospitality | 2019 |
| J&L Campervan Hire and Sales Ltd | Wholesale & retail | 2025 |
| J&M Coffee House Limited | Hospitality | 2023 |
| J. D. Hunter Group Ltd | Extraterritorial | 2018 |
| J. Graham & Sons Ltd | Wholesale & retail | 2022 |
| J. Manning and SON (Dublin) Limited | Construction | 2004 |
| J. S. & E. Farming Limited | Agriculture & fishing | 2017 |
| J. Sloan Contracts Ltd | Construction | 2023 |
| J. Y. Hygiene Supplies Ltd | Wholesale & retail | 2011 |
| J.A Electrics Engineering Ltd | Administrative & support | 2024 |
| J.C. Campbell (N.I.) Limited | Wholesale & retail | 1973 |
| J.C.M.C.B. Limited | Agriculture & fishing | 2013 |
| J.D. Hunter Developments Ltd | Extraterritorial | 2018 |
| J.H Classic Cars Ltd | Wholesale & retail | 2024 |
| J.H. Mckee Limited | Agriculture & fishing | 1947 |
| J.I. Brown Ltd | Agriculture & fishing | 2011 |
| J.K. Fabrications Limited | Manufacturing | 1998 |
| J.K. Structural Ltd | Construction | 2018 |
| J.M Joinery and Construction Ltd | Construction | 2026 |
| J.M. Auto Spares Limited | Wholesale & retail | 2013 |
| J.M. Dismantlers Ltd | Wholesale & retail | 2021 |
| J.M.S Ltd | Construction | 2021 |
| J.Quinn Plumbing and Heating Ltd | Construction | 2003 |
| J.T. Carpets Bessbrook Ltd | Wholesale & retail | 2017 |
| J.T.B. Investment Co. Ltd | | 1989 |
| J30 Cafe Ltd | Hospitality | 2021 |
| Jack Kay's Bar Limited | Hospitality | 2023 |
| Jack Murphy Jewellers Ltd | Wholesale & retail | 2023 |
| Jackpot Films Limited | Information & communication | 2019 |
| Jacqni Ltd | Information & communication | 2018 |
| Jade Garden 2025 Ltd | Hospitality | 2025 |
| Jaguartimingni Limited | Arts & recreation | 2016 |
| Jalt Consulting Ltd | Other services | 2012 |
| JAM Prospects Ltd | Extraterritorial | 2013 |
| James Fitzpatrick Fuels Ltd | Wholesale & retail | 2021 |
| James Green Plastering Contractor Ltd | Construction | 2006 |
| James Hughes Transport Limited | Transport & logistics | 1995 |
| James Jones Agency Limited | Real estate | 2020 |
| James O'Rourke Holdings Limited | Financial services | 2023 |
| James Tolland & Company Limited | Wholesale & retail | 1964 |
| Jamesland Farm Ltd | Agriculture & fishing | 2017 |
| Jamie Carroll Fitness Ltd | Arts & recreation | 2020 |
| Jamtina Limited | Financial services | 2024 |
| Jaramas Investments NI Limited | Construction | 2013 |
| Jarsula Investments Limited | | 1998 |
| Jason Mckeown Equine Tooth Care Ltd | Professional & scientific | 2025 |
| Jattan Food Ltd | Hospitality | 2025 |
| Jattan Investment Ltd | Financial services | 2025 |
| JB Process Engineering Ltd | Professional & scientific | 2022 |