| J Hogg Plastering Ltd | Construction | 2025 |
| J Loughery Electrical Ltd | Construction | 2022 |
| J.P. Mullan Limited | | 1990 |
| JAG Construction (NI) Ltd | | 2006 |
| JAG Optical Ltd | Real estate | 2016 |
| James Court Management Company 2021 Ltd | Households | 2021 |
| James O'Hara & Sons Limited | Wholesale & retail | 1994 |
| James Patrick Homes Limited | Construction | 2015 |
| James Wray Farms Ltd | Agriculture & fishing | 2016 |
| JC Conn Consulting Limited | Information & communication | 2012 |
| Jellymeadow Cabin Company Ltd | Construction | 2021 |
| Jellymeadow Construction Company Ltd | Construction | 2018 |
| Jellymeadow Ltd | Construction | 2012 |
| Jessica Nails Ltd | Other services | 2025 |
| Jewrn Limited | Real estate | 2025 |
| JHM Property Limited | Real estate | 2016 |
| JJC Agencies Limited | Construction | 2023 |
| JJS Artmed Ltd | Health & social care | 2013 |
| JMC Electrics Ltd | Construction | 2024 |
| JMC Inspection Services Ltd | Professional & scientific | 2025 |
| Jmccic Ltd | Real estate | 2025 |
| JMG Contracting Ltd. | Information & communication | 2023 |
| John Street Apartments Ltd | Real estate | 2012 |
| John Thompson M&E Ltd | Construction | 2014 |
| Jordan Recruitment Ltd | Administrative & support | 2025 |
| JSC Contracts (Limavady) Ltd | Construction | 2025 |
| JSC Structures Ltd | Professional & scientific | 2015 |
| Jswap Property Management Ltd | Real estate | 2012 |
| K MAC Construction Ltd | Wholesale & retail | 2015 |
| K MAC Developments Limited | Construction | 2023 |
| K.A.N. Contracts Ltd | Construction | 2015 |
| KAR Build Ltd | Construction | 2023 |
| KAR Contracts Ltd | Construction | 2023 |
| KAR Homes Ltd | Construction | 2023 |
| KAR Rentals Ltd | Real estate | 2025 |
| Karma Event Services Ltd | Administrative & support | 2019 |
| KAT Trading Ltd | Professional & scientific | 2023 |
| Katie’S Corner Ltd | Wholesale & retail | 2018 |
| Kattom Ltd | Construction | 2020 |
| Keady Logistics Ltd | Administrative & support | 2025 |
| Keady Solutions Ltd | Professional & scientific | 2022 |
| KEE Digital Ltd | Information & communication | 2020 |
| Keldon Court Management Company Limited | Households | 2006 |
| Kelly Metal Working Ltd | Manufacturing | 2020 |
| Keomech Engineering Ltd | Construction | 2024 |
| KG Utility Worx Ltd | Construction | 2024 |
| Kilhoyle Holdings Limited | Financial services | 2025 |
| KIN Collaborative Ltd | Wholesale & retail | 2023 |
| KM Car Sales Limited | Wholesale & retail | 2020 |
| KM Contracts Building & Joinery Limited | Construction | 2018 |
| KM1 Properties Ltd | Real estate | 2015 |
| Kmac Plant Hire Ltd | Construction | 2021 |
| KNA Consultancy Services Limited | Professional & scientific | 2021 |
| Knock Road (Ballymoney) Management Company Ltd | Households | 2026 |
| Knocktarna Manor Management Company Limited | Households | 2020 |
| KPM Construction (NI) Limited | Construction | 2011 |
| KS Periodontal Limited | Health & social care | 2024 |
| Ksml Developments Ltd | Construction | 2023 |
| Lackagh Properties Limited | Real estate | 2018 |
| Lajac UK Ltd | Professional & scientific | 2015 |
| Lawncare Services (NI) Limited | Construction | 2014 |
| Lean Cluster NI Ltd | Administrative & support | 2025 |
| Lean Made Simple Ltd | Information & communication | 2022 |
| Leck 9 Trading Ltd | Information & communication | 2015 |
| LEE & Lolo Ltd | Other services | 2025 |
| Leisureni Ltd | Administrative & support | 2021 |
| Lemonade Marketing (N.I.) Ltd | Professional & scientific | 2020 |
| Lettershandoney Management Company Limited | Construction | 2008 |
| LEV Supplies Ltd | Administrative & support | 2005 |
| Lever Court Management Company Limited | Households | 2005 |
| LHS Management Limited | Households | 2018 |
| Like a Rock Ltd | Wholesale & retail | 2023 |
| Limavady Accountancy Services Ltd | Professional & scientific | 2012 |
| Limavady Agri & Build Limited | Wholesale & retail | 2014 |
| Limavady Bells Taxis Ltd | Transport & logistics | 2026 |
| Limavady Business Park Management Limited | Real estate | 2007 |
| Limavady Chiropractic Clinic Ltd | Other services | 2013 |
| Limavady Community Development Initiative Ltd | Other services | 2010 |
| Limavady Day Care Ltd | Health & social care | 2010 |
| Limavady Hardware Company Ltd | Wholesale & retail | 2021 |
| Limavady Irish Whiskey Limited | Wholesale & retail | 2021 |
| Limavady Kitchen Company Ltd | Manufacturing | 2003 |
| Limavady Linen Services Ltd | Other services | 2005 |
| Limavady Memorials Ltd | Manufacturing | 2014 |
| Limavady Road Management Company Ltd | Professional & scientific | 2008 |
| Limestone Close Management Co. Limited | Households | 2026 |
| Lindsay Group Limited | Real estate | 2019 |
| Linen Green Management Company Ltd | Households | 2007 |
| Links View Portrush Limited | Construction | 2015 |
| Liquid Gold Irish Whiskey Limited | Wholesale & retail | 2021 |
| Lisanelly Ltd | Real estate | 2024 |
| Littlepinink Limited | Wholesale & retail | 2023 |
| LJ Fencing Ltd | Public administration | 2025 |
| LJC Leisure Limited | Hospitality | 2022 |
| LJD Fitness Ltd | Other services | 2024 |
| LM Bookkeeping Services Ltd | Professional & scientific | 2019 |
| LMF Electrics Limited | Manufacturing | 2024 |
| LMG TAR Ltd | Construction | 2020 |
| Lodge Court Development Limited | Real estate | 1989 |
| Lodge Mews Management Limited | Households | 2006 |