| JB Bangor Limited | Hospitality | 2025 |
| JB Catering Ltd | Hospitality | 2025 |
| JB EYE Surgery Limited | Health & social care | 2025 |
| JBA Aero Ltd | Manufacturing | 2019 |
| JCH Industrial Ecology Limited | Professional & scientific | 2010 |
| JD Security Solutions (NW) Limited | Administrative & support | 2023 |
| Jemr Logistics Limited | Transport & logistics | 2023 |
| JF Bangor Limited | Hospitality | 2016 |
| JGM Groundworks and Landscaping Ltd | Construction | 2015 |
| JGP1 Consultancy Limited | Professional & scientific | 2023 |
| JH Ecom Ltd | Professional & scientific | 2023 |
| JHT Developments Ltd | Construction | 2026 |
| JIA Catering Ltd | Hospitality | 2025 |
| Jijol Ltd | Hospitality | 2015 |
| Jilkim Properties Ltd | Real estate | 2006 |
| Jill & Stone Limited | Wholesale & retail | 2025 |
| Jjlc Property Ltd | Real estate | 2025 |
| JJS Chippy Ltd | Hospitality | 2026 |
| Jlkl Holdings Ltd | Financial services | 2024 |
| JLM Gardening Ltd | Administrative & support | 2023 |
| JM Brazilian JIU Jitsu Ltd | Arts & recreation | 2017 |
| JMC Legal Services Ltd | Information & communication | 2022 |
| JMF Advisory Ltd | Financial services | 2013 |
| JMK Digital Media Ltd | Information & communication | 2022 |
| JMK Publications Ltd | Information & communication | 2022 |
| JNP Industries Ltd | Professional & scientific | 2024 |
| JNX2 Ltd | Health & social care | 2026 |
| Joan Ross Limited | Wholesale & retail | 2022 |
| John Gould & SON (Bangor) Limited | Wholesale & retail | 1982 |
| John O Williams & SON Funeral Directors Limited | Other services | 2017 |
| John Thompson Ltd | Professional & scientific | 2021 |
| Johnson Trading Private Ltd | Wholesale & retail | 2012 |
| Johnston Property Group Ltd | Households | 2025 |
| Johnston Security Limited | Administrative & support | 2012 |
| Jones a Jones Cyfyngedig | Construction | 1992 |
| Jones and Whitehead Limited | Construction | 1971 |
| Joseph Lawrence & Co (Accountants) Limited | Professional & scientific | 2007 |
| Joycee Akper Ltd | Health & social care | 2024 |
| JP Security & Electrical Ltd | Construction | 2026 |
| JPB (North Wales) Limited | Financial services | 2025 |
| JPS Rentals Ltd | Real estate | 2024 |
| JRC North Wales Ltd | Wholesale & retail | 2019 |
| JRS Engraving Ltd | Other services | 2025 |
| JS Performance Spray Tans Ltd | Other services | 2026 |
| Jsap Belfast Limited | Real estate | 2018 |
| Jsec Ltd | Administrative & support | 2018 |
| Json Codes Limited | Information & communication | 2025 |
| JSP Finance Ltd | Financial services | 2016 |
| JT Kerrswood Limited | Real estate | 2010 |
| JU Jitsu Northern Ireland Ltd. | Education | 2016 |
| Juke Construction (NI) Limited | Construction | 2021 |
| Jungle Book Legion Ltd | Manufacturing | 2022 |
| Just Include Limited | Information & communication | 2025 |
| JWH Ltd | Financial services | 2016 |
| K & J UK Properties Limited | Real estate | 2023 |
| K and B C Ltd | Other services | 2019 |
| K W Jones & SON Limited | Wholesale & retail | 2004 |
| K&D Roofing Solutions Ltd | Construction | 2020 |
| K&N Healthcare Limited | Public administration | 2021 |
| K.S.K Bangor LLP | | 2019 |
| K9 Search and Rescue NI Ltd | Administrative & support | 2019 |
| Ka-Ching Ka-Ching Ltd | Wholesale & retail | 2019 |
| Kajalu Ltd | Arts & recreation | 2015 |
| Kala Developments Limited | Real estate | 2025 |
| Kaleidoscope Gymnastics and Dance Limited | Arts & recreation | 2015 |
| Kaleidoscope K4I Ltd | Information & communication | 2007 |
| Kalye Ltd | Hospitality | 2021 |
| Kalyn Resources Limited | Wholesale & retail | 1999 |
| KAM Catering Ltd | Hospitality | 2024 |
| Kandeh Limited | Manufacturing | 2023 |
| Kanepi Limited | Real estate | 2010 |
| Kare Kabs Taxi Group Ltd | Transport & logistics | 2015 |
| Karlin Properties Limited | Real estate | 2003 |
| Karmann Developments Limited | Construction | 2021 |
| Katsu Asian Belfast Ltd | Hospitality | 2025 |
| KB Flooring Contractors Limited | Construction | 2006 |
| KBC Food Service Ltd | Wholesale & retail | 2011 |
| KE Hong Ltd | Wholesale & retail | 2024 |
| Keane Collective Ltd | Wholesale & retail | 2025 |
| Kebaby Charcoal Limited | Hospitality | 2026 |
| Kebaby House Ltd | Hospitality | 2024 |
| Keeney & Stronge Ltd | Information & communication | 2013 |
| Kehoe Countryside Ltd. | Administrative & support | 2003 |
| Keith Thomas Plumbing & Heating Limited | Construction | 2013 |
| Kelaty House Wembley Limited | Construction | 2018 |
| Kelly Inspection Services Limited | Construction | 2014 |
| Kennedy Wilson Property Ltd | Construction | 2025 |
| Kensington Gate Management Company Limited | Extraterritorial | 1990 |
| Kerr Farm Supplies Limited | Wholesale & retail | 2011 |
| Kestrel Developments Limited | Construction | 2015 |
| Ketford Limited | Mining & quarrying | 2010 |
| Kieran's Automotive Repairs Limited | Wholesale & retail | 2024 |
| Kilcooley Allotments Ltd | Other services | 2010 |
| Kilcooley Community Forum Limited | Other services | 2017 |
| Kilcooley Women's Centre | Education | 2014 |
| Kilgoris Property Ltd | Construction | 2020 |
| Killeen Development Limited | | 1980 |
| Kilmaine Flats Limited | Households | 1979 |
| Kimberley Gulf Limited | Construction | 1989 |
| Kimberley Nails NO1 Ltd | Other services | 2021 |