| Nourish Eatery Ltd | Wholesale & retail | 2023 |
| Nova Education Recruitment Limited | Administrative & support | 2024 |
| Nova Viam Ltd | Administrative & support | 2023 |
| Novaque Ltd | Wholesale & retail | 2018 |
| Novelise Limited | Arts & recreation | 2024 |
| Novofortis Ltd | Health & social care | 2025 |
| Novus REC Ltd | Administrative & support | 2022 |
| Noyce Associates Ltd. | Other services | 1995 |
| NQR Limited | Administrative & support | 2002 |
| NQY Sports Ltd | Hospitality | 2019 |
| NRC Pathology Services Ltd | Health & social care | 2020 |
| NS Events Limited | Hospitality | 2015 |
| NSI Engineering Solutions Ltd | Professional & scientific | 2010 |
| NSI Engineering Solutions Staffing Ltd | Administrative & support | 2011 |
| NSI Industrial O&M Solutions Ltd | Water & waste | 1990 |
| NSI Water and Wastewater Solutions Ltd | Water & waste | 2003 |
| NSN Electrical Ltd | Manufacturing | 2015 |
| Number Seven Gallery Studio Workshop Ltd | Arts & recreation | 2026 |
| Number Seven, Arts, Education and Wellbeing CIC | Arts & recreation | 2026 |
| NW Finance Solutions Ltd | Financial services | 2024 |
| O D R Agri Ltd | Professional & scientific | 2025 |
| O J W Hydrography Ltd | Construction | 2019 |
| O-Region | Arts & recreation | 1998 |
| O. Ogunkoya Services Ltd | Health & social care | 2025 |
| O.F.R. Limited | Wholesale & retail | 2005 |
| Oak & FIR Ltd | Extraterritorial | 2025 |
| Oak Ford Management (Lanhydrock) Limited | Households | 2020 |
| Oakland Energy Ltd | Professional & scientific | 2018 |
| Oakroyd Wood Lane(Falmouth)Management Company Limited(The) | Households | 1970 |
| Oakshott Innovations Ltd | Wholesale & retail | 2025 |
| Oakura Properties Limited | Real estate | 2008 |
| Oatey Media Ltd | Information & communication | 2021 |
| Obic Dental Limited | Financial services | 2024 |
| Obitus Care Limited | Health & social care | 2018 |
| Observatory for Cornwall | Other services | 2000 |
| OC Contracting Ltd | Agriculture & fishing | 2017 |
| OCD FD Ltd | Construction | 2024 |
| Ocean Dental Surgery Limited | Health & social care | 2010 |
| Ocean Gate (Freeholders) Ltd | Households | 2021 |
| Ocean Gate Management Company Limited | Extraterritorial | 2011 |
| Ocean Mountain Co. Ltd | Professional & scientific | 2023 |
| Ocean Plumbing Limited | Construction | 2019 |
| Ocean Reach (Newquay) Ltd | Construction | 2019 |
| Oceanis Apartments Management Company Limited | Households | 2024 |
| Oceanis Management Company Limited | Households | 2007 |
| OCH Operations Truro Limited | Real estate | 2022 |
| OCH Residential Truro Limited | Construction | 2021 |
| Ochre Cafe Ltd | Hospitality | 2026 |
| Octa (U.K.) EOT Ltd | Professional & scientific | 2023 |
| Octa (U.K.) Limited | Wholesale & retail | 1997 |
| Octopus Consultants Ltd | Information & communication | 2021 |
| OFF the Beaten POT Ltd. | Wholesale & retail | 2022 |
| Office & Transport Services Ltd | Transport & logistics | 2009 |
| Offshore Acres Ltd | Construction | 2022 |
| Offshore Insulation Services Ltd | Construction | 2019 |
| Oilconsult Ltd | Professional & scientific | 2006 |
| Okoromai Bay Ltd | Information & communication | 2019 |
| Okumura Partners Limited | Administrative & support | 2020 |
| Olbn Ltd | Health & social care | 2019 |
| Old Chapel Cellars Wine Shop Limited | Wholesale & retail | 2020 |
| Old Chapel Yard Ltd | Real estate | 2025 |
| Oliver Hughes Physiotherapy Ltd | Administrative & support | 2010 |
| Oliver Wilson Property Ltd | Real estate | 2021 |
| OLJ Partners Ltd | Information & communication | 2023 |
| Olly Smith Research and Development Ltd | Information & communication | 2019 |
| Oluna Property Ltd | Construction | 2021 |
| OM Yusuf Limited | Health & social care | 2019 |
| Omega Blue Limited | Professional & scientific | 2018 |
| Omodisun Limited | Financial services | 2025 |
| ON TAP Plumbing & Heating SW Limited | Construction | 2019 |
| Onar Limited | Manufacturing | 2015 |
| Once Upon a Tuesday Ltd | Extraterritorial | 2024 |
| One Pentire Management Company Limited | Households | 2021 |
| One Solar Renewables Limited | Professional & scientific | 2024 |
| One Stop Building Services (SW) Ltd | Construction | 2013 |
| One Wind Renewables Limited | Professional & scientific | 2012 |
| Onshore Property Ltd | Real estate | 2021 |
| Onshore Trading Co Ltd | Other services | 2022 |
| Onshorebuild Limited | Construction | 2025 |
| Open Crossings Ltd | Professional & scientific | 2013 |
| OPN Project Office Limited | Administrative & support | 2017 |
| OPR Plumbing Ltd | Construction | 2025 |
| Optima Health & Performance Ltd | Arts & recreation | 2012 |
| Opusnow Ltd | Professional & scientific | 2017 |
| Oral Alchemy Limited | Health & social care | 2010 |
| Orangutan Trading Co Ltd | Wholesale & retail | 2023 |
| Orbis Software Development Ltd | Wholesale & retail | 2026 |
| Orca Publications Limited | Wholesale & retail | 1994 |
| Orchard Properties Cornwall Limited | Real estate | 2021 |
| Orduna Ltd | Professional & scientific | 2015 |
| Orfi Sports Group Ltd | Administrative & support | 2016 |
| Oriental Care 4 Your Health Limited | Health & social care | 2008 |
| Origin Mining Limited | Mining & quarrying | 2025 |
| Orion Anaesthesia Limited | Health & social care | 2018 |
| Orion Trail Events Ltd | Other services | 2022 |
| Ormshaw Acquisitions Ltd | Real estate | 2023 |
| Ornella Muse Limited | Manufacturing | 2026 |
| Orwin & Algeo Management Solutions Limited | Professional & scientific | 2007 |
| Osborn Enterprises Ltd | Professional & scientific | 2019 |
| Osborn Property Renovations Ltd | Construction | 2022 |