| Hanna Electrical Services Ltd | Construction | 2016 |
| Hanna Tax Consultancy Ltd | Professional & scientific | 2014 |
| Harper Zorrell Limited | Professional & scientific | 2015 |
| Haskey Trading Ltd | Wholesale & retail | 2015 |
| Hawthorn Hill Estate Limited | Agriculture & fishing | 2025 |
| Hendre Property Services Limited | Construction | 2015 |
| Highline Lifts Ltd | Manufacturing | 2019 |
| Hiking Ireland Limited | Administrative & support | 2010 |
| Hollowfarm Animals on Screen N.I Ltd | Agriculture & fishing | 2025 |
| Hollymount Contracts Limited | Wholesale & retail | 2016 |
| Hollymount Homes Ltd | Construction | 2011 |
| Holmestead Saddlery (NI) Limited | Wholesale & retail | 2011 |
| Home-Start Down District | Health & social care | 2005 |
| Home-Start Newcastle Down District | Wholesale & retail | 2018 |
| Homoeopathic Veterinary Supplies Ltd | Agriculture & fishing | 1987 |
| Horizon Design & Build Ltd | Construction | 2026 |
| Htwa Ltd | Information & communication | 2026 |
| HUD Mechanical Ltd | Construction | 2023 |
| Hugh J. O'Boyle Limited | Construction | 1957 |
| Hugh J. O'Boyle Training Ltd. | Other services | 1990 |
| I Dance Irish Ltd | Wholesale & retail | 2012 |
| Icam H Limited | Real estate | 2019 |
| Inch Abbey Holdings Limited | Construction | 2016 |
| Infowing LLP | | 2008 |
| Ingramdavid Consultancy Limited | Other services | 2016 |
| Innovate Networks Limited | Information & communication | 2015 |
| Inspection & Protection Ltd | Other services | 2020 |
| Intelligent Construction Solutions Ltd | Construction | 2019 |
| Intire Fitout Ltd | Construction | 2024 |
| Iona Contracts Ltd | Construction | 2017 |
| Irebeverages Ltd | Wholesale & retail | 2018 |
| Iridium Building Consultancy Limited | Professional & scientific | 2025 |
| Irish Whiskey Bonding Company Limited | Extraterritorial | 2014 |
| Irish Whiskey Bottling Company Limited | Manufacturing | 2023 |
| Ironclad Limited | Real estate | 1992 |
| Island Construction Ltd | Construction | 2026 |
| Island Energy Solutions Ltd | Professional & scientific | 2013 |
| Islataverns Ltd | Hospitality | 2024 |
| J Murphy Sport Horses Ltd | Arts & recreation | 2010 |
| J P Contracts NI Limited | Construction | 2013 |
| J T Transport International Limited | Transport & logistics | 2015 |
| J&M Garden Sheds Ltd | Manufacturing | 2026 |
| J. & W. Mccall Supplies (N.I.) Limited | Wholesale & retail | 1978 |
| Jackson RLJ Ltd | Real estate | 2009 |
| Jacksons of Moira Ltd | Wholesale & retail | 2019 |
| Jacksons of Saintfield Ltd | Wholesale & retail | 2019 |
| JAM Catering (2019) Ltd | Hospitality | 2019 |
| James Glover & Sons Limited | Manufacturing | 1982 |
| James Perry Consulting Limited | Education | 2017 |
| JC 22 Ltd | Manufacturing | 2019 |
| JCC Homes Ltd | Real estate | 2026 |
| JD Subs Limited | Hospitality | 2013 |
| JDS Agri Contracts Limited | Agriculture & fishing | 2012 |
| JEM Autos Ltd | Wholesale & retail | 2016 |
| JFZ Limited | Professional & scientific | 2023 |
| JH Chen 33 Ltd | Hospitality | 2017 |
| JIN Garden Downpatrick Ltd | Hospitality | 2023 |
| Jinbu Corporation Limited | Information & communication | 2017 |
| JJ Donnelly Menswear Ltd | Wholesale & retail | 2012 |
| JJD Rugs Limited | Wholesale & retail | 2016 |
| Jmcg Electrical Services Limited | Construction | 2024 |
| JMT Joinery (IRE) Ltd | Construction | 2021 |
| JMT Real Property Solutions Ltd | Real estate | 2024 |
| Joes Auto Shop Ltd | Wholesale & retail | 2021 |
| Johnston's Property Services Ltd | Households | 2026 |
| Jono Holdings UK Ltd | Professional & scientific | 2018 |
| Joterce Limited | Extraterritorial | 1992 |
| JP Imports Ltd | Wholesale & retail | 2025 |
| Jumpack Limited | Manufacturing | 2014 |
| Kablitz Ltd | Arts & recreation | 2019 |
| KAP Properties (Ardglass) Limited | Construction | 2025 |
| KAP Properties Ltd | Construction | 2011 |
| Katie Marija's Kitchen Ltd | Hospitality | 2026 |
| Kaylee's Kidzone Limited | Health & social care | 2023 |
| Kazadoodle Ltd | Arts & recreation | 2025 |
| KBE Contracts Ltd | Construction | 2019 |
| KC Skip Hire & Recycling Limited | Water & waste | 2023 |
| KCP Creations Ltd | Information & communication | 2016 |
| Kearney Catering Ltd | Hospitality | 2010 |
| Kebble Properties Limited | Households | 2025 |
| KED Electrics Ltd | Construction | 2019 |
| Kelly Solutions (NI) Limited | Information & communication | 2007 |
| Kellys Properties Limited | Construction | 2019 |
| Kennedy Electrical Services Ltd | Manufacturing | 2016 |
| Keystone Provisions Ltd | Wholesale & retail | 2026 |
| KFS Cafes Limited | Hospitality | 2018 |
| KFW Property Ltd | Construction | 2024 |
| KG Strategies Ltd | Professional & scientific | 2019 |
| Kilbridge Properties Limited | | 2006 |
| Kildare Street Apartments Management Limited | Real estate | 2003 |
| Kildrum Enterprises Limited | Wholesale & retail | 2018 |
| Killough Oysters Ltd | Agriculture & fishing | 2003 |
| Killough Youth & Community Hall | Other services | 1999 |
| Killyleagh Community Shop Limited | Extraterritorial | 2004 |
| Killyleagh Development Association Limited | Real estate | 1994 |
| Kilmacrew Properties Limited | Real estate | 2014 |
| Kinelarty Limited | Administrative & support | 2018 |
| Kingdom Healthcare Limited | Professional & scientific | 2006 |
| Kingsfield Equine Veterinary Services Ltd | Professional & scientific | 2017 |
| KIT Room (N.I.) Ltd | Manufacturing | 2018 |