| JRM33 Limited | Information & communication | 2023 |
| JRW Farming Ltd | Agriculture & fishing | 2026 |
| JSW (Yorkshire) Limited | Manufacturing | 2017 |
| JTA Trading Ltd | Information & communication | 2025 |
| Just for Dogs Daycare Northallerton Ltd | Other services | 2022 |
| Just Networks UK Ltd | Information & communication | 2001 |
| JW 4X4 Limited | Wholesale & retail | 2012 |
| JWR Commercial and Plant Repairs Ltd | Manufacturing | 2014 |
| K B B Home Installations Ltd | Construction | 2015 |
| K Commercials Limited | Real estate | 2025 |
| Kalamar Ltd | Information & communication | 2026 |
| Karbec Limited | Administrative & support | 2004 |
| Kash KAT Limited | Professional & scientific | 2024 |
| Kathryn ROE Psychotherapy & Counselling Ltd | Health & social care | 2025 |
| KD Horse Ambulances Limited | Professional & scientific | 2012 |
| Keen Engineering Limited | Manufacturing | 2012 |
| Keeton Developments Limited | Real estate | 2024 |
| KEN Smith Timber Limited | Wholesale & retail | 2012 |
| Kerfoot CS | Financial services | 2015 |
| Kevin Noonan Ltd | Financial services | 2014 |
| Kingdom Services Limited | Administrative & support | 2000 |
| Kirby Cottages Limited | Real estate | 2021 |
| Kirby House Management Company Limited | Households | 2004 |
| Kirkby Fleetham Haulage Limited | Transport & logistics | 1972 |
| Kirkby Fleetham Storage Limited | Administrative & support | 1981 |
| Kose’S Kitchen Ltd | Hospitality | 2023 |
| KP Premier Care Ltd | Health & social care | 2021 |
| Krys Inspections Ltd | Professional & scientific | 2021 |
| KSL Transport Logistics Ltd | Transport & logistics | 2025 |
| KSL Transport Services Ltd | Transport & logistics | 2016 |
| Kumfi Canine Products Limited | Manufacturing | 1998 |
| Kutchenhaus Northallerton Limited | Wholesale & retail | 2021 |
| Kwong Tung Ltd. | Hospitality | 2016 |
| KWS Development Ltd | Professional & scientific | 2012 |
| KYM White Ltd | Administrative & support | 2025 |
| L & D Construction | Construction | 2004 |
| L & O Properties Limited | Real estate | 2007 |
| L a Baines Developments Limited | Construction | 2026 |
| L Bar Coffee Limited | Hospitality | 2026 |
| Lake Henry Ltd | Hospitality | 2022 |
| Landscape Agency Limited | Professional & scientific | 1998 |
| Landwork Limited | Wholesale & retail | 1986 |
| Langbaurgh Engineering Limited | Professional & scientific | 2022 |
| Lark House Limited | Agriculture & fishing | 2019 |
| Laser Clay Shooting Ltd | Arts & recreation | 2025 |
| Laverton Oaks (Kirby Malzeard) Management Company Limited | Real estate | 2025 |
| Lavingham Planning Consultants Limited | Public administration | 2016 |
| Lawton Geophysical Surveys Limited | Administrative & support | 2025 |
| Leases Farming Ltd | Agriculture & fishing | 2013 |
| LED CNC Limited | Wholesale & retail | 2022 |
| LEE Slater Limited | Construction | 2025 |
| Leger Park Limited | Real estate | 1998 |
| Legion Security Solutions Ltd | Administrative & support | 2025 |
| Lemon Helmsley Ltd | Wholesale & retail | 2023 |
| Lenstay Management Limited | Households | 1984 |
| LES Race Builders Limited | Construction | 2014 |
| Level UP (Nationwide) Ltd | Arts & recreation | 2025 |
| Leven Investments Limited | Real estate | 1992 |
| Leven Pastures (Stokesley) Management Company Limited | Real estate | 2025 |
| Lewis & Cooper Limited | Wholesale & retail | 1903 |
| Lewis Webster Machinery Limited | Administrative & support | 2025 |
| LF Building Limited | Construction | 2024 |
| Lifetime Home Improvements Limited | Construction | 1984 |
| Lightfoot Plumbing & Heating Limited | Construction | 2010 |
| Lime Caviar Ltd | Hospitality | 2022 |
| Limekent Limited | Arts & recreation | 1985 |
| Link Vehicle Assistance A1 Limited | Arts & recreation | 1987 |
| Lions Accountants Limited | Professional & scientific | 2008 |
| Lionserv Ltd | Professional & scientific | 2026 |
| Lisa's Cafe Takeaway Limited | Hospitality | 2024 |
| Little Tanner (NE) Ltd | Hospitality | 2019 |
| Living Fire Centre Ltd | Construction | 2022 |
| LIZ Rees Coaching & Training Ltd | Other services | 2017 |
| LJS Holdings Ltd | Households | 2024 |
| Ljwc Limited | Health & social care | 2015 |
| LMS Engineers Ltd | Construction | 2023 |
| Locom Ltd | Wholesale & retail | 2023 |
| Logan's Letting's Limited | Hospitality | 2022 |
| Logans Electrics (NE) Limited | Construction | 2026 |
| Logans Electrics Limited | Construction | 2019 |
| Logyx Ltd | Wholesale & retail | 2022 |
| Londonderry Forge Supplies Ltd | Wholesale & retail | 2011 |
| Londonderry Safe Secure Storage Ltd | Administrative & support | 2026 |
| Lonely Business Ltd | Wholesale & retail | 2022 |
| Loving Your Smile Limited | Health & social care | 2025 |
| LOW Plain Properties Ltd | Real estate | 2026 |
| LR Farming Ltd | Real estate | 2023 |
| LSB Search Limited | Administrative & support | 2025 |
| Lumenshifter Ltd | Information & communication | 2025 |
| Lumsden Capital Limited | Financial services | 2013 |
| Lumsden Partners Limited | Professional & scientific | 2013 |
| Luna Intelligence Limited | Information & communication | 2026 |
| Lusstech Limited | Professional & scientific | 2014 |
| LUXE4LESS Ltd | Wholesale & retail | 2017 |
| Luxori Interiors Limited | Wholesale & retail | 2026 |
| Lyons & Co (Northallerton) Ltd | Professional & scientific | 2018 |
| M Davis Construction Services Ltd | Professional & scientific | 2019 |
| M Dobson Ltd | Construction | 2018 |
| M Preston Plumbing & Heating Limited | Construction | 2022 |
| M T POT Ltd | Financial services | 2025 |