| I & GT Property Investment Ltd | Real estate | 2025 |
| I T Carpentry Limited | Construction | 2007 |
| I.S.B.D. Limited | Information & communication | 1987 |
| IAN Balchin Ltd | Transport & logistics | 2015 |
| IAN Palfreyman Consulting Limited | Professional & scientific | 1998 |
| IAN Wood Engineering Limited | Professional & scientific | 2002 |
| Iceworks Ltd | Professional & scientific | 2024 |
| Iconnecthq Ltd | Information & communication | 2025 |
| IIK Property Services Limited | Other services | 2012 |
| Iken Consulting Limited | Real estate | 1995 |
| Iken Press Limited | Information & communication | 2025 |
| Illuminate Resources Limited | Administrative & support | 2024 |
| Imagine Everything Limited | Information & communication | 2024 |
| Imagine Together Ltd | Administrative & support | 2023 |
| Imperial Motorcycles Ltd | Administrative & support | 2018 |
| IMS Wealth Ltd | Financial services | 2014 |
| IN Villam Ltd | Professional & scientific | 2025 |
| Independent Care Limited | Health & social care | 2007 |
| Inderwick Equestrian Activities Limited | Arts & recreation | 2017 |
| Inderwick Investments Limited | Real estate | 2005 |
| Indigo Entertainment Limited | Information & communication | 1998 |
| Indigo Marmoset Limited | Professional & scientific | 2014 |
| Industriel Techniques Limited | Manufacturing | 2002 |
| Infamous Travel Co. Ltd | Administrative & support | 2025 |
| Infinity Inns Limited | Hospitality | 2019 |
| Inframous Ltd | Professional & scientific | 2019 |
| Inkerman Ipswich Ltd | Real estate | 2022 |
| Innovation Park Management Limited | Real estate | 2005 |
| Innventure Vacation Services Limited | Hospitality | 2016 |
| Inovex Ltd | Manufacturing | 2019 |
| Inside Associates Ltd | Information & communication | 2009 |
| Inspired Mortgage Solutions Limited | Professional & scientific | 2016 |
| Inspired Renovations Fram Ltd | Construction | 2016 |
| Insulated Conservatory Co Ltd | Construction | 2024 |
| Intego Corporate Ltd | Wholesale & retail | 2012 |
| Integra Composites Limited | Administrative & support | 2003 |
| Integrated Ideas Agency Limited | Information & communication | 2013 |
| Intelligence Technologies Limited | Other services | 2008 |
| Inteq Limited | Professional & scientific | 2017 |
| Invelarochay Properties Limited | Real estate | 1984 |
| Invisible MAN Productions Limited | Information & communication | 2019 |
| IP Properties (Suffolk) Ltd | Real estate | 2020 |
| IP Twelve Limited | Households | 2016 |
| Ipswich Computer Services Ltd | Information & communication | 2002 |
| Ipswich Croquet Club Ltd | Arts & recreation | 2021 |
| Ipswich Mortgage Services Limited | Financial services | 2005 |
| Ipswich Plumbing & Heating Services Ltd | Extraterritorial | 2014 |
| Ipswich Together CIC | Health & social care | 2024 |
| Irgm Limited | Construction | 2022 |
| Iris Carr Restorations Limited | Other services | 2008 |
| Iron Will Studios Ltd. | Administrative & support | 2008 |
| Isaacs Barbershop Limited | Administrative & support | 2017 |
| Isbiso Limited | Professional & scientific | 2018 |
| Iswim (Suffolk) Ltd | Education | 2013 |
| Iswim Limited | Arts & recreation | 2013 |
| IT Stratus Limited | Information & communication | 2012 |
| Italian Homes Limited | Real estate | 2013 |
| Itts - Inter'L Teaching and Training Services Limited | Hospitality | 2014 |
| IVY Lodge Partnership Limited | Construction | 2016 |
| J Barry Ltd | Construction | 2023 |
| J D C C (East Anglia) Ltd | Administrative & support | 2012 |
| J Norman Builder Ltd | Construction | 2023 |
| J'S Fish & Chips Limited | Hospitality | 2002 |
| J.J Mitchell and A.D Mitchell Limited | Other services | 2024 |
| J.M Enterprises Limited | Real estate | 2014 |
| J.S Motor Mechanic Ltd | Wholesale & retail | 2019 |
| J.W. Crick Limited | Administrative & support | 2023 |
| J.W.J Morris (Holdings) Ltd | Financial services | 2018 |
| J.W.J.Morris Limited | Real estate | 1962 |
| JA Lawrence Limited | Professional & scientific | 2019 |
| Jack Properties Ltd | Construction | 2016 |
| Jackson Barnes 2010 Limited | Administrative & support | 2010 |
| Jackson Road Management Limited | Households | 1985 |
| Jact Wellness Ltd | Education | 2020 |
| JAI Yachting Limited | Extraterritorial | 2023 |
| James Hanley Management Ltd | Households | 2021 |
| James Kininmonth Limited | Manufacturing | 2019 |
| Jameson Marshall Limited | Professional & scientific | 2003 |
| Jamie & Partners Property Consultancy Ltd | Construction | 2013 |
| Jane Webb Marketing Limited | Professional & scientific | 2003 |
| Jasper Corporation Limited | Agriculture & fishing | 1997 |
| Jastac Limited | Hospitality | 2013 |
| Jay.C. Homes Ltd. | Construction | 1980 |
| JBE Electrical Ltd | Construction | 2025 |
| JDM Rigging Services Ltd | Construction | 2024 |
| Jelcaf Ltd | Information & communication | 2009 |
| Jennycaresolutions Limited | Health & social care | 2026 |
| Jetmore Developments Limited | Real estate | 2005 |
| JFK Media Limited | Information & communication | 2025 |
| JFW Agritech Ltd | Financial services | 2022 |
| Jhmg Construction Ltd | Construction | 2025 |
| JJ Designs (EA) Limited | Administrative & support | 2002 |
| JL Plumbing Services Ltd | Construction | 2013 |
| JLJ Property Investments Limited | Real estate | 2020 |
| JM Aesthetics Nurse Ltd | Health & social care | 2026 |
| JME252 Limited | Professional & scientific | 2019 |
| JMS Practice Limited | Health & social care | 2019 |
| Joannes Commerical Cleaning Ltd | Other services | 2026 |
| Joannes Deep Cleaning Ltd | Other services | 2026 |
| Joanne’S Cleaning Services Ltd | Other services | 2025 |