| J & S Powder Coating Ltd | Construction | 2016 |
| J a Coyle Manufacturing Limited | Real estate | 2020 |
| J GER Design Ltd. | Construction | 2019 |
| J&P Leisure Limited | Arts & recreation | 2017 |
| J&S Renewables Limited | Construction | 2020 |
| J. Donaghey Construction Ltd | Construction | 1999 |
| J.J. Childcare Ltd | Arts & recreation | 2008 |
| J.J.A.C.E. Ltd | Health & social care | 2012 |
| J.J.A.C.E. Properties Limited | Real estate | 2023 |
| Jack Andrew Foundation | Health & social care | 2020 |
| Jackdaw Developments Ltd | Real estate | 2005 |
| Jackie and Rita Property Ltd | Real estate | 2024 |
| Jade 20 Ltd | Real estate | 2020 |
| Jake & Co 2020 Limited | Other services | 2021 |
| James O'Kane Drylining Ltd | Construction | 2013 |
| Jamison Medical Limited | Health & social care | 2025 |
| JAR Construction Limited | Construction | 2006 |
| Jasmine YM Ltd | Hospitality | 2026 |
| JC Ecoenergy Ltd | Construction | 2023 |
| Jc's Smokehouse Ltd | Hospitality | 2025 |
| JCR Network Services Limited | Professional & scientific | 2009 |
| Jervis Lane Properties Ltd | Real estate | 2024 |
| JG Marine Consultants Limited | Agriculture & fishing | 2016 |
| Jgmc Contracts Limited | Construction | 2021 |
| JH Mechanical & GAS Ltd | Construction | 2025 |
| JJ2CONSULTANCY UK Ltd | Wholesale & retail | 2019 |
| JM Towing & Breakdown Ltd | Transport & logistics | 2024 |
| JMC Drylining Limited | Construction | 2025 |
| Jmcc Builders Ltd | Construction | 2012 |
| Jmcg Engineering Ltd | Construction | 2024 |
| JMD Medical Limited | Health & social care | 2018 |
| JMG Enterprises Limited | Wholesale & retail | 2012 |
| John Byrne Limited | Construction | 2014 |
| John Herron Accountants Limited | Professional & scientific | 2019 |
| John Long Safety Limited | Professional & scientific | 2026 |
| Johnson Produce Ltd | Wholesale & retail | 2000 |
| JOK Drylining Limited | Construction | 2025 |
| Jonah Technologies Limited | Information & communication | 2016 |
| Jonathan Murphy Global Ltd | Professional & scientific | 2023 |
| Jongar Ltd | Real estate | 2015 |
| Joseph Porter Brickwork Ltd | Construction | 2015 |
| JP Timber Frames Ltd | Construction | 2012 |
| JPE Hotels Limited | Hospitality | 2018 |
| JPM Contracts Limited | Construction | 1996 |
| JTR Partitions Ltd | Construction | 2016 |
| Jungle Soft Play Limited | Arts & recreation | 2026 |
| Junos Investments Ltd | Real estate | 2022 |
| Just Content Studios Ltd | Information & communication | 2021 |
| KAM Waters Ltd | Agriculture & fishing | 2017 |
| Kandy Kiosk Ltd | Wholesale & retail | 2021 |
| Kania Developments Limited | Construction | 2015 |
| Kara Irish Pottery Ltd | Manufacturing | 2008 |
| Karem Limited | Professional & scientific | 2019 |
| Kaylas Plant Hire Limited | Professional & scientific | 2014 |
| KBM Electric Ltd | Financial services | 2026 |
| KBT Power Distribution Limited | Construction | 2025 |
| KCD Donegal Holdings Ltd | Financial services | 2026 |
| KDC Investments | Construction | 2019 |
| Keith Gurney Ltd | Construction | 2014 |
| Kelantan Ltd | Professional & scientific | 1999 |
| Kemb Holdings Limited | Financial services | 2024 |
| Kenneth Gallagher Haulage Limited | Transport & logistics | 2017 |
| Kevin Cullen Transport UK Limited | Transport & logistics | 2017 |
| Kevin Finan Opticians Limited | Health & social care | 2003 |
| Kevin Mcgrath Trading Limited | Construction | 2025 |
| KGD Electrical Ltd | Extraterritorial | 2024 |
| Kids N' Kinship Limited | Other services | 2015 |
| Killew Management Ltd | Financial services | 2013 |
| Kinnea Builders Limited | Construction | 2016 |
| Kirion Developments Ltd | Construction | 2021 |
| Kirion Homes Ltd | Construction | 2020 |
| Kiwi and Copper Limited | Manufacturing | 2021 |
| Kleenan Land & Properties (UK) Limited | Real estate | 2024 |
| Kmac Builders Ltd | Construction | 2022 |
| Kmac Trading Limited | Wholesale & retail | 2016 |
| KMC Tyres Limited | Wholesale & retail | 2014 |
| KMC Wealth Management Ltd | Financial services | 2017 |
| Kmconnect Limited | Wholesale & retail | 2018 |
| Kmcs Properties Ltd | Real estate | 2025 |
| KML Distributors Limited | Wholesale & retail | 2019 |
| KPR Consultants Ltd | Professional & scientific | 2022 |
| KSK Group Holding Limited | Financial services | 2024 |
| KSK Rathmor Engineering & Recruitment Ltd | Construction | 2023 |
| KSM Autos Limited | Wholesale & retail | 2023 |
| KT Electrical & Security Ltd | Manufacturing | 2024 |
| Kylemore Enterprises Limited | Real estate | 2005 |
| L G Joinery Ltd | Construction | 2026 |
| L Synnott Electrical Ltd | Construction | 2026 |
| L.Hegarty Engineering Limited | Professional & scientific | 2025 |
| LA Paints & Interiors (NI) Limited | Wholesale & retail | 2016 |
| LA Sosta Limited | Hospitality | 1995 |
| LAB Autobody Ltd | Wholesale & retail | 2025 |
| Labs Value Limited | Wholesale & retail | 2014 |
| LAC Manufacturing Europe Ltd | Manufacturing | 2025 |
| Lagan Grange Company Limited | Extraterritorial | 2016 |
| Landed Gentry Limited | Real estate | 2002 |
| Larcastle | Administrative & support | 2019 |
| Leadcare Healthcare Limited | Health & social care | 2024 |
| Leafair Community Association Ltd | Other services | 2019 |
| Leafair Sport and Recreational C.I.C. | Education | 2012 |