| J K R Properties Limited | Real estate | 2004 |
| J Mccabe & SON Ltd | Wholesale & retail | 2003 |
| J. & a. Murphy Ltd | Real estate | 1995 |
| J.C. Boustead & SON Limited | | 1961 |
| James Carnduff & Sons (Builders) Limited | Real estate | 1967 |
| James G. Mcalorum, Limited | Construction | 1961 |
| James Geddis (Contractors) Limited | Construction | 1975 |
| James Knox & Sons Limited | Wholesale & retail | 1960 |
| James Mckee Coffey & Sons Fishing Ltd | Agriculture & fishing | 2006 |
| James Turner Engineering Limited | Manufacturing | 2002 |
| Janos Developments Limited | Construction | 1997 |
| Jasper Investments Limited | Real estate | 1998 |
| Jemphrey International Limited | Wholesale & retail | 2004 |
| JMG Mechanical Services Ltd | Construction | 2003 |
| JMN Trading Limited | Construction | 1989 |
| JOE Hanna's Limited | Wholesale & retail | 2007 |
| John Fisher (NI) Ltd | Agriculture & fishing | 2003 |
| John Haugh Limited | Construction | 2007 |
| John Kearney Limited | Manufacturing | 1974 |
| John Lambe Plant Hire Limited | Construction | 2016 |
| John Shilliday Ltd | Wholesale & retail | 2002 |
| Jones, Peters Consultancy Services Limited | Extraterritorial | 1983 |
| Joseph Walls Ltd | Wholesale & retail | 2002 |
| Kary Hill Properties Limited | Real estate | 1988 |
| Kearney Trawlers Ltd | Agriculture & fishing | 2007 |
| Keelryan Developments Ltd | Construction | 2006 |
| Kellys Golf Centre Limited | Arts & recreation | 2007 |
| Kennedy Engineering Services (NI) Limited | Construction | 2003 |
| KF (Management) Limited | Hospitality | 2003 |
| Kildare Quay Management Company Limited | Real estate | 2001 |
| Kilkeel Kippering Co. Limited | Manufacturing | 1977 |
| Kilkeel Seafoods Limited | Manufacturing | 1961 |
| Killinchy and District Motor Cycle Club Limited | Arts & recreation | 1959 |
| Killowen Shellfish Limited | Wholesale & retail | 2009 |
| Kinney Recycling Ltd | Water & waste | 2008 |
| Klass Stockhouse Limited | Real estate | 1983 |
| Knockmore Hill Property Management Ltd | Construction | 2005 |
| KPS Inns Limited | Hospitality | 2004 |
| KX Bidco Limited | Financial services | 2025 |
| KX Software Limited | Information & communication | 1996 |
| L Burns Limited | Wholesale & retail | 2003 |
| LA Styling Ltd | Other services | 2008 |
| Labrofish Exports Limited | | 1990 |
| Lacranvey Limited | Hospitality | 2005 |
| Laurel Cottage Ltd | Information & communication | 2002 |
| Lawnfield Grove Management Company Limited | Households | 2002 |
| Lecale Developments Limited | Real estate | 2003 |
| Leestone Sand & Gravel Limited | Mining & quarrying | 2003 |
| LI' S Palace BT25 Limited | Hospitality | 2023 |
| Lisbarnett and Lisbane Community Association Limited | Other services | 1999 |
| Little Kingdom Kids Limited | Health & social care | 2015 |
| Lloyd Technical Services Limited | Professional & scientific | 1987 |
| Loftus Properties Limited | Real estate | 1979 |
| Lomac Construction Ltd | Construction | 2003 |
| Long Term Care (Ireland) Limited | | 1999 |
| Loughorne Limited | Professional & scientific | 2003 |
| Loughview Taverns Limited | Real estate | 1963 |
| Lygala Limited | Households | 2003 |
| M G a Communication Limited | Information & communication | 1994 |
| M&M Trucks Limited | Wholesale & retail | 2009 |
| Mackeown Trading Limited | Wholesale & retail | 1973 |
| Madoc Agencies Limited | | 1997 |
| Maghera Developments Limited | Construction | 2000 |
| Magill Enterprises Limited | Professional & scientific | 2000 |
| Mcallister Bros Limited | Water & waste | 1987 |
| Mcalorum Holdings Limited | Professional & scientific | 2007 |
| Mcbennett Developments Ltd | Construction | 2003 |
| Mcbran Developments Ltd | Wholesale & retail | 2006 |
| Mcevoys Limited | Wholesale & retail | 1997 |
| Mcgreevy Shops Limited | Wholesale & retail | 1991 |
| Mckevitt Services Limited | Wholesale & retail | 1986 |
| Mcmaster Engineering Limited | Manufacturing | 2006 |
| MCN Automation Ltd | Manufacturing | 2002 |
| MED Construction Limited | Construction | 2000 |
| Michael Dunlop Limited | Construction | 1990 |
| Microberi Ltd | Households | 2005 |
| Milltown Electrical Wholesale Limited | Wholesale & retail | 1995 |
| Millvale Services Limited | Wholesale & retail | 1992 |
| Minders Limited | Wholesale & retail | 2004 |
| Minorca Developments Management Company Limited | Construction | 2002 |
| MM Euro Limited | | 2004 |
| Modern Times (Northern Ireland) Limited | Real estate | 1995 |
| Morton Commercials Ltd | Wholesale & retail | 2005 |
| Mother Hubbert Day Care Nursery Limited | Health & social care | 1997 |
| Motis Ireland Limited | Transport & logistics | 2002 |
| Mould Designer Ltd | Manufacturing | 2000 |
| Mount Mills (NI) Limited | Manufacturing | 2009 |
| Mourne Electrical Services Limited | Construction | 2008 |
| Mourne Satellite Consultancy Limited | Information & communication | 2012 |
| Mournesports Limited | Arts & recreation | 1996 |
| Movilla House Limited | Health & social care | 1988 |
| Moyadd Holdings Limited | Professional & scientific | 2006 |
| Moyfab Engineering Limited | Manufacturing | 1994 |
| Mulkerns Eurospar Limited | Wholesale & retail | 2009 |
| Mullaghboy Limited | Health & social care | 2005 |
| Mullaghfernaghan Property Limited | Extraterritorial | 2000 |
| Multiflow Limited | Real estate | 1991 |
| Murray Car & Commercial Repairs Ltd | Wholesale & retail | 2006 |
| Musicbest Limited | | 2001 |
| N & R Gordon Ltd | Wholesale & retail | 2003 |