| JB Motor Sales Ltd | Wholesale & retail | 2025 |
| JBR Energy Holdings Limited | Extraterritorial | 2026 |
| Jbrh Limited | Real estate | 1970 |
| JD Industrial Cleaning Ltd | Administrative & support | 2025 |
| Jdoutdoors Ltd | Construction | 2025 |
| JEF Commercial Ltd | Real estate | 2023 |
| JEF Holdings Ltd | Financial services | 2021 |
| JEF Trading Ltd | Information & communication | 2017 |
| Jeftex Builders Limited | Construction | 1986 |
| Jerts V Ltd | Manufacturing | 2023 |
| Jester Brothers International Ltd | Information & communication | 2017 |
| JMG Yates Engineering Ltd | Professional & scientific | 2022 |
| JMR Business Consultancy Ltd | Professional & scientific | 2024 |
| Jones and Morrell Ltd | Construction | 2015 |
| Jones and Morrell Properties Limited | Real estate | 2026 |
| Jones Bros Ruthin (Infrastructure) Co Limited | Construction | 2019 |
| Jones Bros Ruthin Co Limited | Administrative & support | 1970 |
| Jones Bros Ruthin Development Holdings Limited | Financial services | 2018 |
| Jones Bros. Ruthin (Civil Engineering) Co. Limited | Construction | 1970 |
| Jones Bros. Ruthin (Farms) Co. Limited | Agriculture & fishing | 1985 |
| Jones Rental Limited | Real estate | 2016 |
| Josh Angell Ltd | Administrative & support | 2016 |
| JTW Tool Hire and Sales Ltd | Manufacturing | 2026 |
| Just Investment Strategies Limited | Financial services | 2004 |
| K & R Training Limited | Education | 2017 |
| Karizma Barber Ruthin Ltd | Other services | 2025 |
| Kartre Limited | Construction | 2014 |
| Kerbpower Ltd | Manufacturing | 2022 |
| Kolourful Unique Limited | Other services | 2024 |
| KTL Contracting Limited | Transport & logistics | 2007 |
| L E Jones Hauliers Ltd | Transport & logistics | 2010 |
| L.A.W. Consulting Limited | Professional & scientific | 2021 |
| L.E. Jones Holdings Limited | Professional & scientific | 2000 |
| L.E. Jones Limited | Transport & logistics | 1987 |
| L.E.Jones International Limited | Extraterritorial | 1982 |
| Landlinked CIC | Professional & scientific | 2024 |
| Lavinia Stamps Limited | Wholesale & retail | 2013 |
| Leading Sales Limited | Professional & scientific | 2025 |
| LEE Properties Corwen Ltd | Real estate | 2018 |
| Lettings & Properties Limited | Real estate | 2003 |
| Lewis & Hunter Contracting Limited | Construction | 2004 |
| Lexie Consulting Ltd | Administrative & support | 2017 |
| Leyland Arms Country Retreats Ltd | Hospitality | 2022 |
| LIG Accounting Ltd | Professional & scientific | 2016 |
| Livtu Group Ltd | Information & communication | 2022 |
| Llanbenwch Ltd | Hospitality | 2021 |
| Lleweni Parc Limited | Arts & recreation | 1991 |
| Lloyd Farming Ltd | Agriculture & fishing | 2023 |
| Llys YR Orsedd Management Company Limited | Households | 2024 |
| Lolligo Events Ltd | Other services | 2023 |
| Longriver Consulting Ltd | Information & communication | 2024 |
| LOX Box Ruthin Limited | Other services | 2025 |
| LR Films Limited | Information & communication | 2024 |
| Luna Estates and Property Management Ltd | Real estate | 2023 |
| M E D Evans Ltd | Real estate | 2024 |
| M.W.S. (Ruthin) Limited | Manufacturing | 1990 |
| M.Wright Properties Ltd | Real estate | 2025 |
| Maenol Estates Limited | Real estate | 2003 |
| Maes Truan Farm Limited | Agriculture & fishing | 2012 |
| Maes Truan Limited | Agriculture & fishing | 2012 |
| Marinepro Manpower Services Limited | Professional & scientific | 2024 |
| Mark Gittins Consulting LLP | | 2023 |
| Marketing & Internet Services Limited | Professional & scientific | 2010 |
| Martin Roberts & SON Building and Joinery Contractors Limited | Construction | 2005 |
| Mauseloch Properties Ltd | Real estate | 2017 |
| Mauve Cymru Ltd | Professional & scientific | 2023 |
| Mayfive Equipment Limited | Wholesale & retail | 1992 |
| Mcknight's Forestry & Landscaping Ltd | Agriculture & fishing | 2023 |
| Mercher Ltd | Wholesale & retail | 2023 |
| Method Marketing Group Ltd | Professional & scientific | 2026 |
| MH Wind Service Ltd | Professional & scientific | 2023 |
| Millbell Environmental Ltd | Wholesale & retail | 2014 |
| Mind Bloom Limited | Health & social care | 2020 |
| Minffordd Accountancy Ltd | Professional & scientific | 2024 |
| Miri Meithrin CYF | Health & social care | 2016 |
| MJR GAS Ltd | Construction | 2020 |
| MNC Developments Ltd | Construction | 2025 |
| Monster Grill Events Ltd | Hospitality | 2023 |
| Monster Grill Takeaways Ltd | Hospitality | 2026 |
| Moonjoon Kennels Ltd | Other services | 2023 |
| Moonjoon Nutrition Ltd | Extraterritorial | 2018 |
| Moonstone Consulting Limited | Information & communication | 2023 |
| Morfa Bach CYF | Hospitality | 2025 |
| Morgan Venables Ltd | Professional & scientific | 2018 |
| Morris and ME Ltd | Wholesale & retail | 2025 |
| Moseley Homes NW Ltd | Real estate | 2023 |
| Mother Mountain Productions C.I.C. | Information & communication | 2016 |
| Moto Dealer Network Ltd | Professional & scientific | 2026 |
| Mottram Properties Ltd | Administrative & support | 2004 |
| MPH Rentals Ltd | Real estate | 2025 |
| MRS Versey's Acupuncture Ltd | Health & social care | 2023 |
| MSL Motor Vehicle Preparations Ltd | Wholesale & retail | 2011 |
| Muddy Steps Ltd | Health & social care | 2025 |
| Muir Consulting Limited | Information & communication | 2024 |
| Mulberry House Management Company Limited | Households | 2005 |
| Mull Projects Ltd. | Professional & scientific | 2014 |
| N K Project Management Limited | Construction | 2012 |
| Nails by Samm Ltd | Other services | 2025 |
| Naturally Ethical Ltd | Wholesale & retail | 2018 |
| Naturally Ethical Rhuthun Limited | Wholesale & retail | 2024 |