| JEC Holdings Limited | Extraterritorial | 2022 |
| Jeeveport Limited | | 1983 |
| Jejg Ltd | Health & social care | 2024 |
| Jesan Limited | Real estate | 2014 |
| Jewellery HUT Enterprises Ltd | Wholesale & retail | 2022 |
| JF Mcgovern Contracts Limited | Administrative & support | 2003 |
| JG Crushing and Recycling Limited | Water & waste | 2006 |
| JGR Properties NI Limited | Construction | 2017 |
| Jiang Sweet Chilli Ltd | Hospitality | 2018 |
| JJ Plant Sales Limited | Wholesale & retail | 2018 |
| JJM Connect Ltd | Professional & scientific | 2023 |
| JJT Rentals & Developments Ltd | Construction | 2020 |
| JK Wholesale & Creative Ltd | Wholesale & retail | 2025 |
| JKB Consulting Engineers Ltd | Professional & scientific | 2016 |
| JKB Hydrobike & Watersport Imports Limited | Wholesale & retail | 2020 |
| JKL Rentals Limited | Real estate | 2023 |
| JM Joinery N. Ireland Ltd | Construction | 2017 |
| JMC Music Ltd | Arts & recreation | 2024 |
| JMC Poultry Ltd | Agriculture & fishing | 2015 |
| JMC Renewables IRL Ltd | Energy | 2013 |
| JME (NI) Ltd | Construction | 2014 |
| JMJ Commercial Ltd | Real estate | 2024 |
| Joanne Knowles Medical Writing Ltd | Professional & scientific | 2010 |
| John Courtney Tree Surgery Ltd | Administrative & support | 2014 |
| John D Brennan Ltd | Construction | 2003 |
| John K. Cathcart Limited | Wholesale & retail | 1985 |
| John Mckeegan Funeral Undertaker Limited | Other services | 2017 |
| John O'Brien Architectural Consultants Ltd | Professional & scientific | 2004 |
| John Richardson (E) Limited | Wholesale & retail | 1980 |
| Johnston Agri Ltd | Agriculture & fishing | 2022 |
| Johnston and Logue Bricklaying Ltd | Construction | 2025 |
| Johnston Paving Ltd | Construction | 2026 |
| Johnstown Farms Ltd | Agriculture & fishing | 2004 |
| Johny's Restaurant Limited | Hospitality | 2023 |
| Jones Finance Limited | Financial services | 1983 |
| Jones Property Developments Limited | Construction | 2004 |
| Jones Surveying Services Ltd | Professional & scientific | 2024 |
| Jonny Gibson Memorial Classic CIC | Health & social care | 2025 |
| Jonny Wilson Group Limited | Extraterritorial | 2022 |
| Jordan Breen Art Ltd | Arts & recreation | 2024 |
| Joy Riding Bikes Ltd | Wholesale & retail | 2026 |
| Joymount Properties Limited | Real estate | 2006 |
| JP FOY Properties Limited | Real estate | 2025 |
| JR Farms Limited | Agriculture & fishing | 2015 |
| JR NI Cars Limited | Wholesale & retail | 2025 |
| JS Operations Ltd | Financial services | 2022 |
| Jspb Enterprises Limited | Arts & recreation | 2022 |
| JT Engineering Supplies Ltd | Wholesale & retail | 2026 |
| Judra Limited | Financial services | 2019 |
| K Donohoe Transport Ltd | Transport & logistics | 2022 |
| K LEE (Contracts) Ltd | Agriculture & fishing | 2015 |
| K Tierney Commercials Ltd | Wholesale & retail | 2021 |
| K&G Housing Limited | Real estate | 2026 |
| K&V International Ltd | Wholesale & retail | 2025 |
| K-Vend Services Limited | Hospitality | 2023 |
| K9KUTZ Ltd | Agriculture & fishing | 2024 |
| KAA Properties Limited | Real estate | 1998 |
| Kane Music Limited | Arts & recreation | 2015 |
| Karen Bennett Educational Psychology Services Ltd | Education | 2025 |
| Karl Mcgowan Motors Ltd | Wholesale & retail | 2022 |
| Karn UK Limited | Hospitality | 2021 |
| KB Laundry Solutions Limited | Manufacturing | 2015 |
| KBL Jointing Ltd | Construction | 2020 |
| KC Exports Ltd | Wholesale & retail | 2023 |
| KCC Whelan Contracts Ltd | Administrative & support | 2017 |
| Kdee Limited | Construction | 2024 |
| Kdfc Limited | Agriculture & fishing | 2011 |
| Keady Farms Ltd | Wholesale & retail | 2024 |
| Kearns Civils Ltd | Construction | 2025 |
| Keenan Group Ltd | Construction | 2025 |
| Keep Moving Property Ltd | Real estate | 2025 |
| Keep ‘ER LIT Events Ltd | Administrative & support | 2019 |
| Kelly Rahill & Company Limited | Professional & scientific | 2012 |
| Kelly Wind Energy Ltd | Energy | 2012 |
| Keltic Flavour Band Limited | Arts & recreation | 2019 |
| Keogh & Co Business Consultants Ltd | Professional & scientific | 2017 |
| Kern Dent Limited | Health & social care | 2016 |
| Kerona Scientific (UK) Ltd | Professional & scientific | 2022 |
| Kesh Enterprise Company Limited | Real estate | 1992 |
| Kettyle Consultancy Limited | Manufacturing | 2013 |
| KGM Business Management Limited | Professional & scientific | 2017 |
| KHM Properties (Number 2) Limited | Real estate | 2014 |
| KHM Properties Limited | Real estate | 2006 |
| Kiernan Agri Contracts Ltd | Agriculture & fishing | 2019 |
| Kiernan Plant Hire Ltd | Construction | 2010 |
| Kilcoa Ltd | Agriculture & fishing | 2026 |
| Killadeas Quarry Management Company Limited | Water & waste | 2012 |
| Killaghy Eggs Limited | Agriculture & fishing | 2025 |
| Killard Farms Ltd | Agriculture & fishing | 2024 |
| Killesher Community Development Association | Other services | 1998 |
| Killeter Wind Limited | Energy | 2020 |
| Killshank Trading Solutions Limited | Administrative & support | 2015 |
| Killyhevlin Hotel Limited | Hospitality | 1962 |
| Killymitten Wind Limited | Energy | 2014 |
| Kilmore Jetworks Lisnaskea Ltd | Transport & logistics | 2025 |
| Kilmore Jetworks Ltd | Transport & logistics | 2003 |
| Kilturk Enterprises Ltd | Wholesale & retail | 2025 |
| Kilwest Transport Limited | Transport & logistics | 2013 |
| Kinawley Community Hall Association | Construction | 2008 |
| Kinawley Enterprise Limited | Health & social care | 2002 |