| John O'Boyle (Contracts) Limited | Construction | 2014 |
| John Quinn, Limited | Extraterritorial | 1925 |
| Johnny Cornflakes Coleraine Limited | Hospitality | 2016 |
| Johnny Cornflakes Portstewart Limited | Hospitality | 2016 |
| Jonathan Hanna Consulting Ltd | Professional & scientific | 2026 |
| Joocy Ltd. | Information & communication | 2013 |
| JR Engineering (N.I.) Ltd | Water & waste | 2015 |
| JRC Cars Ltd | Wholesale & retail | 2015 |
| JRD Commercial & Residential Cleaning Limited | Administrative & support | 2025 |
| JRG Property Developments Limited | Construction | 2023 |
| JRH Group Ltd | Wholesale & retail | 2021 |
| Jsvl Ltd | Information & communication | 2025 |
| JTF Consultancy Ltd | Professional & scientific | 2025 |
| Jtmm Holdings Limited | Financial services | 2021 |
| JUA Holdings Limited | Professional & scientific | 2025 |
| Judith Keys Limited | Administrative & support | 2019 |
| Jungle Pets Ltd | Wholesale & retail | 2020 |
| JW (Carnlough) Limited | Agriculture & fishing | 2025 |
| JWM Planning Limited | Professional & scientific | 2022 |
| K & G Mcatamney (Wholesale Meats) Limited | Manufacturing | 2012 |
| K & G Mcatamney Butchery & Deli Limited | Wholesale & retail | 2006 |
| K&A Ecom Limited | Wholesale & retail | 2024 |
| K-Scape Ltd | Administrative & support | 2015 |
| K-Team Racing Limited | Arts & recreation | 2017 |
| Ka-Boom Properties Ltd | Real estate | 2022 |
| Kaizen Core Limited | Professional & scientific | 2021 |
| Kaldi Dungannon Ltd | Hospitality | 2026 |
| Kaldi Portstewart Ltd | Hospitality | 2026 |
| Kann O&M Ltd | Manufacturing | 2020 |
| Karakkattu Limited | Health & social care | 2023 |
| Karingmore Homes Limited | Health & social care | 2013 |
| Karlmac Media Ltd | Information & communication | 2009 |
| Katie Smith Aesthetics Ltd | Other services | 2020 |
| KB Cladding and Facades Ltd | Construction | 2025 |
| KBE Limited | Manufacturing | 2006 |
| Kbmm Property Management Ltd | Households | 2020 |
| KD Repairs Ltd | Wholesale & retail | 2023 |
| KD Towers Roofing Ltd | Construction | 2017 |
| KDA Ferguson Ltd | Agriculture & fishing | 2026 |
| KDT Property Holdings Ltd | Real estate | 2025 |
| Kearney's Ltd | Information & communication | 2025 |
| Kebab Palace Ballymena Ltd | Hospitality | 2024 |
| Keep Cool Refrigeration Ltd | Manufacturing | 2023 |
| Keeperco Ltd | Wholesale & retail | 2024 |
| Keith a Dinsmore Ltd | Professional & scientific | 2017 |
| Kells & Connor Community Improvement Association | Other services | 2011 |
| Kells Auto Paint & Supplies Limited | Wholesale & retail | 2023 |
| Kellstown Farm Limited | Agriculture & fishing | 2023 |
| Kellswater Stables Ltd | Other services | 2023 |
| Kelly Civil & Utilities PTY Ltd | Construction | 2020 |
| Kelly Exterior Cleaning Ltd | Administrative & support | 2025 |
| Kelly Mcauley Ltd | Other services | 2017 |
| Kempston Contracts Limited | Professional & scientific | 2019 |
| Kenlin Investments Limited | Administrative & support | 1961 |
| Kennedy Laboratories Ltd | Health & social care | 2021 |
| Kennedy's Pharmacy Limited | Health & social care | 2013 |
| Kenneth Brown Financial Services Ltd | Other services | 2005 |
| Kenny Taylor Ltd | Hospitality | 2023 |
| Kenvara Services Limited | Households | 1992 |
| Kernohan Construction Ltd | Construction | 2004 |
| Kerr Agnew Electrical Services Limited | Construction | 2025 |
| Kerr Pilates Physio Limited | Health & social care | 2024 |
| Kevin Brogan (Plumbing & Heating) Ltd | Construction | 2019 |
| Keycor Land Limited | Real estate | 2017 |
| KFM Group Ltd | Construction | 2022 |
| KG Commercials Limited | Real estate | 2009 |
| KH Bakery Ltd | Wholesale & retail | 2024 |
| Khayber Galgorm Ltd | Hospitality | 2023 |
| Kico UKI Ltd | Hospitality | 2018 |
| Kids Cars (N.I.) Limited | Wholesale & retail | 2020 |
| Kidz Farm Ltd | Arts & recreation | 2026 |
| Kilbride Farms Ltd | Agriculture & fishing | 2018 |
| Kilcurry Holding Ltd | Financial services | 2019 |
| Kildrum Developments Ltd | Construction | 2020 |
| Killane Properties Limited | Real estate | 2006 |
| Killeen Manor Management Company Limited | Households | 2017 |
| Killycoogan Properties Limited | Real estate | 1994 |
| Killycowan Road 1979 Limited | Extraterritorial | 2015 |
| Killycrot Estates Limited | Real estate | 2012 |
| Killyflugh Farm Eggs Ltd | Agriculture & fishing | 2026 |
| Kilmore Country House Ltd | Hospitality | 2017 |
| Kiloy Developments Limited | Construction | 2002 |
| Kinkead Consulting Services Ltd | Professional & scientific | 2016 |
| Kintra Tours Ltd | Transport & logistics | 2025 |
| Kirkenny Farm Ltd | Education | 2020 |
| Kitchen Beats Limited | Hospitality | 2021 |
| Kittagh Limited | Financial services | 2017 |
| KLC Ocular Prosthetics Ltd | Health & social care | 2022 |
| Klew Chew Limited | Real estate | 2023 |
| Knockan Holdings Limited | Real estate | 2015 |
| Knockdene Health Care Ltd | Administrative & support | 2017 |
| Knockdene Homecare Ltd | Administrative & support | 2020 |
| Knowehead Poultry Limited | Agriculture & fishing | 2018 |
| Knowles Poultry Limited | Agriculture & fishing | 2020 |
| Knox Electrical Limited | Construction | 2011 |
| Koinonia John the Baptist Ireland | Other services | 2013 |
| Koomsd 7 Ltd | Hospitality | 2023 |
| Kopczynski Ltd | Construction | 2026 |
| Kore Building Services Ltd | Construction | 2015 |
| L Donnelly & Co (N.I.) Limited | Professional & scientific | 2020 |