| Jolly Fry'R Fast Foods Ltd | Hospitality | 2021 |
| Joph Holdings Ltd | Real estate | 2023 |
| Jordan Contracts Ltd | Construction | 2015 |
| Jordan Energy Solutions Limited | Construction | 2015 |
| Joyx Ltd | Professional & scientific | 2023 |
| JSF Builders Ltd | Construction | 2001 |
| Jump Lanes Trampoline Parks Limited | Arts & recreation | 2018 |
| JW Service Centre Ltd | Wholesale & retail | 2011 |
| JWA (Promotional Products) Limited | Professional & scientific | 2004 |
| K a Magherafelt Limited | Construction | 2013 |
| K J Trading Company Limited | Wholesale & retail | 1997 |
| KAB Flooring Limited | Construction | 2012 |
| Kaem Holdings Ltd | Professional & scientific | 2020 |
| Kaigan Community Interest Company | Hospitality | 2019 |
| Kamin (Coleraine) Ltd | Wholesale & retail | 2018 |
| Kane Ecology Ltd | Professional & scientific | 2018 |
| Karegan House Management Ltd | Households | 2016 |
| Karolina White Beauty Studio Ltd | Other services | 2026 |
| Kartsport Leisure Ltd | Arts & recreation | 2019 |
| Keady Quarry Ltd | Mining & quarrying | 2014 |
| Kearney Homes Limited | Construction | 2021 |
| Kearney Residential Ltd | Real estate | 2026 |
| Kenny Mcintyre & SON Ltd | Construction | 2017 |
| Kennys Foodfare Limited | Extraterritorial | 2021 |
| Kensington Estates (NI) Ltd | Construction | 2004 |
| Keomin Solutions Ltd | Mining & quarrying | 2025 |
| Kfit Ltd | Real estate | 2025 |
| Kgmb Holdings Ltd | Financial services | 2020 |
| Khanikhail Holdings Ltd | Real estate | 2024 |
| Kian Construction Group Ltd | Construction | 2025 |
| Kielt Dartry Ltd | Health & social care | 2025 |
| Kilbride Bay Ltd | Professional & scientific | 2005 |
| Kilda 2 | Professional & scientific | 2024 |
| Kildrum Services Limited | Households | 2020 |
| Killane Mews Management Company Ltd | Extraterritorial | 2016 |
| Killymuck Holdings Limited | Other services | 2017 |
| Kilmakee Hall Management Company Limited | Households | 2022 |
| Kilrea Service Station Ltd | Wholesale & retail | 1994 |
| Kilrock Limited | Construction | 2019 |
| Kingdom Play Ltd | Arts & recreation | 2018 |
| Kingsgate Renewal Ltd | Real estate | 2013 |
| Kitty Loves Ltd | Wholesale & retail | 2021 |
| KM2 Contracts Limited | Construction | 2018 |
| Knitting Craft (Coleraine) Limited | Real estate | 1976 |
| Knockanboy Lane Management Company Limited | Households | 2026 |
| Knockbann Holdings Limited | Financial services | 2023 |
| Knockcarlow Properties Ltd | Real estate | 2019 |
| Knockertootin Holdings Limited | Financial services | 2022 |
| Knockintern Developments Ltd. | Real estate | 2016 |
| Knocklynn Land Management Ltd | Extraterritorial | 2014 |
| Knowehead Land Management Ltd | Real estate | 2003 |
| Knox Pure Projects Ltd | Construction | 2022 |
| Korben Development Ltd | Real estate | 2025 |
| KT Fleet Solutions Ltd | Manufacturing | 2025 |
| KT Trucks Ltd | Manufacturing | 2021 |
| KW Agri Supplies Ltd | Agriculture & fishing | 2015 |
| Kyoujin Fight Academy Coleraine C.I.C. | Other services | 2021 |
| L Allison & Sons Ltd | Real estate | 2025 |
| L&J 2022 Ltd | Construction | 2022 |
| Lacpatrick Dairies (NI) Limited | Manufacturing | 2015 |
| Lakeside Courtyard Management Company Limited | Extraterritorial | 2012 |
| Lamex Foods Europe (N.I.) Ltd | Wholesale & retail | 2006 |
| Lamont Property Limited | Real estate | 2026 |
| Lamont Stone Limited | Wholesale & retail | 1996 |
| LAN Rentals Limited | Real estate | 2025 |
| Lanes Office Supplies Ltd | Wholesale & retail | 2002 |
| Larden Meadows Management Company Ltd | Households | 2019 |
| Laurel Hill Business Park Limited | Real estate | 2019 |
| Laurel Hill House Limited | Real estate | 2019 |
| Laurel Mews Residents Ltd | Households | 2024 |
| Laurelvale Farm Ltd | Agriculture & fishing | 2021 |
| Laverty Eyecare Limited | Wholesale & retail | 2024 |
| Laze N Relax Ltd | Arts & recreation | 2019 |
| LCP Global Limited | Education | 2021 |
| LDY NI Ltd | Administrative & support | 2022 |
| LE Foyer DES Artistes CIC | Arts & recreation | 2021 |
| LED Stairs Coleraine Ltd | Construction | 2023 |
| Lenamore Park Management Company Limited | Extraterritorial | 2008 |
| Lenamore Productions Ltd | Administrative & support | 2022 |
| Lhwang Ltd | Wholesale & retail | 2024 |
| Libertyapp Ltd | Information & communication | 2024 |
| Lillys at the Diamond Ltd | Hospitality | 2019 |
| Linchuanqing Limited | Wholesale & retail | 2023 |
| Linen Park (Portadown) Management Ltd | Households | 2020 |
| Linenhall Hearing Ltd | Wholesale & retail | 2025 |
| Links (Castlerock) Management Company Limited - the | Households | 2000 |
| Lisdale Mews Management Co Ltd | Households | 2005 |
| Lisderg Property Management Limited | Households | 2018 |
| Lisnagort Court Management Company Limited | Households | 2021 |
| Lisnamonaghan Meadows Management Co Ltd | Households | 2014 |
| Lisroan Management Limited | Households | 2023 |
| LIT Energy Systems Limited | Manufacturing | 2023 |
| LIT Photography Ltd | Professional & scientific | 2025 |
| Little Acorns Playgroup | Education | 2001 |
| LJ Andrews Limited | Professional & scientific | 2025 |
| Lockbox Storage N.I. Limited | Transport & logistics | 2020 |
| Lodge Grove Management Company Limited | Households | 2020 |
| Lodge Road Management Limited | Extraterritorial | 1995 |
| Lodge Road Property Partnership | | 2003 |
| Lodge Road Property Partnership Eight LP | | 2007 |