| JP Morgan Enterprises Limited | Real estate | 2003 |
| JPB Electrical Compliance N.I. Ltd | Manufacturing | 2025 |
| JPB Electrical N.I. Ltd | Construction | 2025 |
| JRB Driving Ltd | Transport & logistics | 2016 |
| Jump Into More Wonders Ltd | Wholesale & retail | 2025 |
| Junapril Ltd | Wholesale & retail | 2025 |
| Just for Dogs Carrickfergus Ltd | Other services | 2025 |
| JW Motor Factors Ltd | Wholesale & retail | 2023 |
| JWJ Engineering Ltd | Manufacturing | 2015 |
| Jymkidz Ltd | Education | 2026 |
| K & D Property Renovations Ltd | Construction | 2026 |
| K (N.I.) Law Limited | Professional & scientific | 2015 |
| K L Interior Design Ltd | Professional & scientific | 2024 |
| K&K Ecom Limited | Wholesale & retail | 2025 |
| K&L Catering (NI) Ltd | Hospitality | 2014 |
| K. Thompson Electrical 1982 Limited | Construction | 2014 |
| K.C. (N.I.) Development Ltd | Administrative & support | 2016 |
| KA Aviation Ltd | Manufacturing | 2022 |
| Kaishan-Gbi Limited | Manufacturing | 2026 |
| Kaleido Digital Trading Ltd | Wholesale & retail | 2025 |
| Kamakura Restaurant Carrick NI Ltd | Hospitality | 2021 |
| Kane Properties & Developments Ltd | Construction | 1991 |
| KDL Trading Ltd | Wholesale & retail | 2010 |
| Kelley Courtney Hair Design Ltd | Other services | 2012 |
| Kelly's TAP Room Limited | Hospitality | 2015 |
| Ketchup Design Ltd | Manufacturing | 2014 |
| KG609 Ltd | Real estate | 2020 |
| Kilcreggan Homes | Health & social care | 1984 |
| Kilmore Gate Management Co Ltd | Households | 2017 |
| Kilroot Cafe Ltd | Hospitality | 2025 |
| King Wolf Technology Limited | Information & communication | 2025 |
| Kirkwoods (Funeral Directors) Limited | Extraterritorial | 1987 |
| Kitchen Design Showroom Limited | Wholesale & retail | 2018 |
| Kitten Leaf Friends Ltd | Wholesale & retail | 2025 |
| Kjrm NI Ltd | Other services | 2014 |
| KLC Joinery Ltd | Construction | 2023 |
| Klean Aesthetics by Carol Ltd | Other services | 2024 |
| Kludka Aviation Ltd | Manufacturing | 2016 |
| Kmac Transport Ltd | Administrative & support | 2016 |
| Knightscastle Ltd | Wholesale & retail | 2024 |
| Knockagh Management Limited | Administrative & support | 2011 |
| Knockagh Poultry Limited | Agriculture & fishing | 2013 |
| Knowledgebrics Ltd | Administrative & support | 2024 |
| Kobats Property Limited | Real estate | 2025 |
| KPC Aerosystems Ltd | Manufacturing | 2022 |
| Kragoran Limited | Professional & scientific | 2005 |
| KTK Property Ltd | Real estate | 2019 |
| Kvlr Equipped Ltd | Financial services | 2021 |
| Kvlr Training CIC | Arts & recreation | 2021 |
| L.A.P. Property Developments Limited | Real estate | 2013 |
| L.D. Units Limited | Manufacturing | 1995 |
| LA Bridal House Ltd | Wholesale & retail | 2023 |
| Lambrequin Interiors Ltd | Professional & scientific | 2022 |
| Lancasterian Court Management Ltd | Extraterritorial | 2003 |
| Land Carrier Ltd | Manufacturing | 2025 |
| Landscape and Garden Solutions Ltd | Administrative & support | 2021 |
| Lane 52 Ltd | Professional & scientific | 2018 |
| Laragh's Croft Management Limited | Households | 2011 |
| Larne Motor Club Limited | Arts & recreation | 1956 |
| Laser Spoke Limited | Manufacturing | 2012 |
| Laurel Lodge Management Company Limited | Real estate | 1987 |
| Laurelhill Newtownabbey Limited | Households | 2014 |
| Lauryn James Ltd | Wholesale & retail | 2019 |
| LCI Engineering Services Ltd | Manufacturing | 2026 |
| Leading Governance Ltd | Professional & scientific | 2013 |
| Lecale Consulting Ltd | Construction | 2025 |
| LEE Thomson Services Ltd | Professional & scientific | 2026 |
| Lennox 1961 Limited | Extraterritorial | 2015 |
| Lewis Mews Block D Management Company Limited | Households | 2023 |
| Lewis Mews Block E Management Company Limited | Households | 2023 |
| Lewis Square Development Management Company Limited | Households | 2003 |
| LFF Management Ltd | Transport & logistics | 2016 |
| LH Nails & Spa Ltd | Other services | 2023 |
| Lichfield Management Company Ltd | Households | 2008 |
| Lightscan Ltd | Extraterritorial | 1996 |
| Limestone Management Limited | Households | 2006 |
| Linenhall Consulting LLP | | 2022 |
| Linkadrink Ltd | Information & communication | 2020 |
| Lionswood Estates Ltd | Construction | 2017 |
| Lisabella Flowers Ltd | Wholesale & retail | 2024 |
| Lislaynan Apartment Management Company Limited | Hospitality | 2005 |
| Lisleen 2012 LLP | | 2012 |
| Lisnagrilly Hall (2) Management Limited | Households | 2017 |
| Lisnagrilly Hall Management Limited | Households | 2007 |
| Little GEM Grocery Limited | Wholesale & retail | 2023 |
| Little Moments Coffee Roaster Ltd | Manufacturing | 2024 |
| Ljmfitout Limited | Construction | 2025 |
| LK Financial Solutions Ltd | Financial services | 2025 |
| Lmf-Gbi Limited | Manufacturing | 2021 |
| Lmkc Holdings Ltd | Real estate | 2024 |
| Lmrm Limited | Hospitality | 2024 |
| Lock Property & Security Services Ltd | Construction | 2020 |
| LOK Analysis Limited | Information & communication | 2025 |
| Lord Harry Commercial Properties Ltd | Real estate | 2014 |
| Lough Mourne Properties Ltd | Administrative & support | 2023 |
| Lough Mourne Refurbs Ltd | Administrative & support | 2024 |
| Loughmourne Wind Limited | Energy | 2015 |
| Loughshore Homes Ltd | Construction | 2021 |
| Loughview Auto Repairs Limited | Wholesale & retail | 2018 |
| Loughview Village Apartment Management (Carrickfergus) Limited | Households | 2023 |