| Heathmount Development Management Company Limited | Households | 2000 |
| Henry Livestock Ltd | Wholesale & retail | 2026 |
| Henry Plant Sales International Ltd | Wholesale & retail | 2016 |
| Hensons Ltd | Construction | 1996 |
| Hera Holdings Ltd | Financial services | 2026 |
| Hiex Derry Operations Limited | Hospitality | 2018 |
| Higcas Properties Limited | Construction | 2004 |
| Higgins Car Dismantlers Ltd | Water & waste | 2006 |
| Higgins Carparts Ltd | Wholesale & retail | 2015 |
| Higgins Properties & Investments Ltd | Construction | 2024 |
| Highview Portstewart Management Company Limited | Households | 2008 |
| Hillmans Court Management Company Limited | Extraterritorial | 2004 |
| HM Business Ventures Ltd | Wholesale & retail | 2025 |
| Hollytree Car Sales Ltd | Wholesale & retail | 2021 |
| Holme Farm Limited | Agriculture & fishing | 2016 |
| Home-Start Causeway | Health & social care | 2005 |
| Hope Macaulay Limited | Wholesale & retail | 2020 |
| Houston Tate Limited | Agriculture & fishing | 2016 |
| HPS Enterprises NI Ltd | Wholesale & retail | 2025 |
| Hqme Limited | Mining & quarrying | 2014 |
| HRA 666 Ltd | Hospitality | 2023 |
| Hugh Wade & SON Ltd | Other services | 2019 |
| Hullabaloos Restaurant Ltd | Hospitality | 2017 |
| Hungry Apple Limited | Hospitality | 2015 |
| Hutchinson Contracts Ltd | Construction | 2013 |
| Hutchinson Group Holdings (NI) Ltd | Manufacturing | 2014 |
| Hutchinson Holdings Garvagh Ltd | Households | 2019 |
| Hutton Drive Property Management Company Ltd | Households | 2017 |
| Hyde Park DAM Limited | Construction | 2015 |
| Hygienics Plus Ltd | Administrative & support | 2025 |
| I-55 Investments Limited | Real estate | 2023 |
| I4W Promotions Ltd | Extraterritorial | 2014 |
| IAN Millar Fabrications Ltd | Manufacturing | 2007 |
| IAS Consulting Ltd | Information & communication | 2023 |
| Icann Coaching Ltd | Arts & recreation | 2025 |
| Iconic Street Dance Ltd | Education | 2025 |
| ICT316 Ltd | Other services | 2012 |
| IDS Wealth Management LLP | | 2008 |
| IJC Agricultural Limited | Financial services | 2018 |
| Illuminaire Leadership Limited | Professional & scientific | 2022 |
| Impatient Pictures Ltd | Information & communication | 2020 |
| Imperial Hotel Garvagh Ltd | Hospitality | 2019 |
| Indulge Dessert Bars Ltd | Wholesale & retail | 2026 |
| Infotax Ltd | Professional & scientific | 2010 |
| Innisfree Investments Limited | Real estate | 1963 |
| Innisfree Investments NO 1 Limited | Financial services | 2010 |
| INNOV8 Events Group Limited | Hospitality | 2021 |
| Innovation Incubation and Implementation Company Ltd | Extraterritorial | 2011 |
| Innovative Parking Ltd | Extraterritorial | 2016 |
| Inovento Factory Limited | Manufacturing | 2021 |
| Insurebrands Limited | Financial services | 2014 |
| International Growth Consultancy Ltd | Professional & scientific | 2016 |
| Iora Network Limited | Professional & scientific | 2022 |
| Ireland Generators & Spare Parts Ltd | Manufacturing | 2014 |
| Irish Centre for Operational Leadership Limited | Education | 2024 |
| Isabella Lingerie Ltd | Wholesale & retail | 2017 |
| Isarc Limited | Information & communication | 2010 |
| Isonomia Limited | Information & communication | 2024 |
| Isovisuals Ltd | Professional & scientific | 2022 |
| Ivan Scott Associates Ltd | Professional & scientific | 2014 |
| Ivan Wilson Holdings Limited | Financial services | 2021 |
| Ivan Wilson Limited | Wholesale & retail | 2016 |
| Ivansons Holdings Limited | Wholesale & retail | 2021 |
| Ivor's Transport Ltd | Transport & logistics | 2020 |
| Ivory Bridal Ltd | Wholesale & retail | 2018 |
| J & E Bell Limited | Real estate | 2025 |
| J & N Demolitions Ltd | Construction | 2015 |
| J a Humphrey & Sons Ltd | Real estate | 2026 |
| J&R Retail Ltd | Wholesale & retail | 2016 |
| J&S Project 2 Limited | Other services | 2025 |
| J&S Services IRE Limited | Other services | 2023 |
| J.A. Humphrey Limited | Agriculture & fishing | 1998 |
| Jacunda | Construction | 1990 |
| Jade Investments 2020 Limited | Construction | 2019 |
| JAI HO JAI Ltd | Wholesale & retail | 2018 |
| Janas Cars Ltd | Wholesale & retail | 2022 |
| Jane Leadon Ltd | Professional & scientific | 2018 |
| Jasmine Asian Massage & Spa Ltd | Health & social care | 2025 |
| Jazz Horses Limited | Agriculture & fishing | 2016 |
| JB Autos (Coleraine) Limited | Wholesale & retail | 2017 |
| JC Construction Services Ltd | Professional & scientific | 2001 |
| Jdoc Holdings Ltd | Financial services | 2025 |
| Jeda Development Limited | Financial services | 2011 |
| Jeda Investments Ltd | Construction | 2014 |
| Jeda Power Limited | Manufacturing | 2012 |
| Jehovah Jireh Ltd | Health & social care | 2025 |
| Jersey Island Estates LP | | 2006 |
| JF Travel (Portrush) Ltd | Administrative & support | 2025 |
| JH Retail Ltd | Hospitality | 2021 |
| Jigsaw House Limited | Education | 2025 |
| Jj's Accessories Limited | Wholesale & retail | 2011 |
| JLM Castlerock Ltd | Wholesale & retail | 2023 |
| JM Promos Ltd | Administrative & support | 2021 |
| JMH Plant Mobilisation Services Limited | Manufacturing | 2020 |
| JML Electrical (N.I.) Limited | Construction | 2024 |
| JMM Fire and Security Ltd | Administrative & support | 2017 |
| JMS Metaltec Ltd | Manufacturing | 2014 |
| Jody Tolan Carpets Ltd | Construction | 2023 |
| John Holmes Engineering Ltd | Professional & scientific | 2023 |
| Jola Engineering (N.I.) Limited | Construction | 2011 |