| JHM Gray Consulting Limited | Professional & scientific | 2026 |
| Jimmy MAY Scrap Metal Limited | Water & waste | 2005 |
| JJ Central Heating and Plumbing Ltd | Construction | 2023 |
| Jjmm Consulting Ltd | Professional & scientific | 2026 |
| JJS Composites Ltd | Manufacturing | 2019 |
| JM GEO Consulting Ltd | Professional & scientific | 2023 |
| JO Peel Studio Ltd | Arts & recreation | 2024 |
| Joey Anna Textile Design Limited | Professional & scientific | 2016 |
| John Kent Limited | Real estate | 2001 |
| Jonathan Cunliffe Ltd | Real estate | 2017 |
| Jones & Jones Estates Cornwall Ltd | Real estate | 2023 |
| Jones & Jones Estates Ltd | Financial services | 2022 |
| Jones Negys Ltd | Financial services | 2024 |
| Joseph Waller Properties Limited | Real estate | 2014 |
| Joyful Journeys Childcare LLP | | 2023 |
| Joèl B Consulting Ltd | Administrative & support | 2023 |
| JP Coatings Ltd | Administrative & support | 2016 |
| JR Construction Cornwall Ltd | Construction | 2026 |
| JRF Airworthiness Consulting Ltd | Professional & scientific | 2025 |
| JRJ Cleaning Ltd | Administrative & support | 2020 |
| JS Vantage Tech Ltd | Information & communication | 2025 |
| JSR Developments (Cornwall) Limited | Construction | 2016 |
| JTM Pension Consulting Limited | Professional & scientific | 2026 |
| Jukwa Limited | Information & communication | 2011 |
| Julia Evans Accountants Ltd | Professional & scientific | 2012 |
| Jumunjy Ltd | Hospitality | 2017 |
| Junglefowl Games Ltd | Manufacturing | 2025 |
| Just Blueberri Limited | Wholesale & retail | 2026 |
| Just Delights Cornwall Ltd | Wholesale & retail | 2013 |
| Just Delights Property Limited | Real estate | 2022 |
| K & M Builds Ltd | Real estate | 2022 |
| K&M Lettings (SW) Ltd | Real estate | 2023 |
| Kanom Thai Ltd | Hospitality | 2024 |
| Kastel Collection Limited | Real estate | 2020 |
| Kauri & Oak Ltd | Manufacturing | 2022 |
| Kawaida Therapy CIC | Education | 2025 |
| KDB Pubs Ltd | Hospitality | 2025 |
| KDT Building Services Limited | Construction | 2007 |
| Keelson Maritime Holdings UK Limited | Administrative & support | 2024 |
| Keelstone Management Limited | Real estate | 2025 |
| Keeping IT Balanced Ltd | Professional & scientific | 2017 |
| Kegs With Legs Limited | Hospitality | 2010 |
| Kemsley Consulting Ltd | Information & communication | 2026 |
| Kepla (Design) Ltd | Wholesale & retail | 2020 |
| Kernick Metal Finishers Limited | Construction | 2002 |
| Kernow Agronomy (SW) Ltd | Agriculture & fishing | 2023 |
| Kernow Controls Ltd | Information & communication | 2010 |
| Kernow Fire & Electrical Services Ltd | Construction | 2025 |
| Kernow Fisheries Limited | Wholesale & retail | 2008 |
| Kernow Marine Consultants Limited | Professional & scientific | 2012 |
| Kernow Marine Solutions Limited | Professional & scientific | 2022 |
| Kernow Medical Supplies Limited | Wholesale & retail | 2003 |
| Kernow Minds CIC | Education | 2025 |
| Kernow Psychiatry Ltd | Health & social care | 2024 |
| Kernow Research Services Limited | Professional & scientific | 2019 |
| Kernow Service Solutions Limited | Manufacturing | 2025 |
| Kernow Technologies Limited | Wholesale & retail | 2026 |
| Kernow Wine Ltd | Wholesale & retail | 2020 |
| Kernowek Kerth Limited | Construction | 2016 |
| KEW HAL an TOW Management Company Limited | Real estate | 2016 |
| Key Asset Holdings Limited | Real estate | 2024 |
| Keynvor Consulting Services Ltd | Administrative & support | 2011 |
| Keynvor Homes Limited | Real estate | 2021 |
| Keynvor Morlift Limited | Administrative & support | 2008 |
| Keynvor Morlift Marine Contractors Ltd | Administrative & support | 2018 |
| Kill the Cat Theatre Ltd | Arts & recreation | 2021 |
| Kiln Sauna Ltd | Other services | 2023 |
| Kimber Court Management Company Limited | Households | 1979 |
| Kimberley Clinic Limited | Health & social care | 2013 |
| Kimberley Croft Limited | Households | 2007 |
| Kind Tide Limited | Information & communication | 2023 |
| King Charles Court Limited | Health & social care | 1996 |
| King Marine Integrity Ltd | Professional & scientific | 2026 |
| Kingdom and Sparrow Ltd | Professional & scientific | 2016 |
| Kingsley Tresidder Funeral Service Ltd | Other services | 2021 |
| Kinnasia Ltd | Hospitality | 2018 |
| Kith & KIN Limited | Administrative & support | 2013 |
| Kliro Capital Investment Management Ltd | Financial services | 2023 |
| Kliro Capital Limited | Financial services | 2020 |
| Kliro Capital Partners Limited | Financial services | 2026 |
| Kliro Capital Private Equity Ltd | Financial services | 2023 |
| Kloth CIC | Administrative & support | 2020 |
| KLS Property Investments LLP | | 2007 |
| KMD Recruitment Limited | Administrative & support | 2020 |
| Koffiji Cornwall Limited | Hospitality | 2025 |
| Koru Properties Limited | Real estate | 2020 |
| Kuishi Ltd | Wholesale & retail | 2018 |
| L J Brown Plumbing and Heating Ltd | Construction | 2025 |
| L M Coulson Limited | Construction | 2007 |
| LA Architecture Ltd | Professional & scientific | 2023 |
| Lacuna Productions Ltd | Information & communication | 2017 |
| Ladron Films Ltd | Information & communication | 2025 |
| Lamanva Training Centre Limited | Other services | 2018 |
| Land Enhancement and Acquisition Partnership Limited | Real estate | 2019 |
| Last Thoughts Online Ltd | Information & communication | 2021 |
| Laura Bell Salon Limited | Other services | 2026 |
| Law Systems Limited | Information & communication | 1992 |
| LBS Estates Ltd | Real estate | 2025 |
| LC Marketing Plus Ltd | Administrative & support | 2010 |
| Leandesk Ltd | Wholesale & retail | 2025 |