| Corfield Cottages Ltd | Real estate | 2024 |
| Cornea Ltd | Professional & scientific | 2022 |
| Coronation Leads Ltd | Information & communication | 2025 |
| Cotswolds Equestrian Ltd | Agriculture & fishing | 2024 |
| Couldrick Consulting Limited | Health & social care | 2023 |
| Counties and Capital Investments Ltd | Real estate | 2024 |
| County Construction (Oxon) Limited | Construction | 2001 |
| County Holdings (Oxon) Ltd | Financial services | 2024 |
| Courage Victor Ltd | Real estate | 2023 |
| Courtyard Agriculture Ltd | Agriculture & fishing | 2009 |
| COX Field Support Ltd | Manufacturing | 2024 |
| Cozy Orangutan Games Ltd | Information & communication | 2025 |
| CR Automotive Group Ltd | Wholesale & retail | 2020 |
| CR Properties & Investments Ltd | Construction | 2026 |
| Crabbe Scaffolding Ltd | Construction | 2023 |
| Createch Limited | Information & communication | 2011 |
| Creature Comfort Home Pet Sitters Limited | Other services | 2014 |
| Credica Limited | Information & communication | 2000 |
| Crescita Group Ltd | Real estate | 2026 |
| Crest Building & Roofing Limited | Construction | 2003 |
| Crossroads Motor Co. Ltd | Wholesale & retail | 2020 |
| CSG Legacy Group Ltd | Real estate | 2025 |
| CSK Avon Ltd | Transport & logistics | 2025 |
| CT Oxfordshire Medics Ltd | Health & social care | 2025 |
| Cuban Salsa Didcot Ltd | Education | 2025 |
| Cyan International | Professional & scientific | 2009 |
| Cygnet Magazines Limited | Information & communication | 2014 |
| D Dunne Ltd | Construction | 2020 |
| D G Services Oxfordshire Ltd | Manufacturing | 2025 |
| D J Matthews Limited | Wholesale & retail | 2012 |
| D. W. Hinchliffe Ltd | Construction | 2006 |
| D2M Ltd | Real estate | 2026 |
| D6 Plastering Ltd | Construction | 2016 |
| DAI Properties Limited | Real estate | 2021 |
| Dameo Limited | Wholesale & retail | 2024 |
| DAN One Associates Ltd | Construction | 2014 |
| Daniel Services Ltd | Construction | 2024 |
| Darass Ltd | Health & social care | 2016 |
| Darcy Medical Ltd | Health & social care | 2024 |
| Dare Warwick (Properties) Limited | Construction | 1955 |
| Darran Richard Brown Ltd | Extraterritorial | 2024 |
| Darshan Datatech Ltd | Information & communication | 2024 |
| DAS 1 Limited | Wholesale & retail | 2021 |
| David Powell Ltd | Professional & scientific | 2022 |
| David Savage Consultancy Ltd | Professional & scientific | 2018 |
| Dawes Developments Limited | Construction | 2016 |
| Dawkins Rail and Construction Ltd | Construction | 2023 |
| DB Arch Ltd | Professional & scientific | 2026 |
| DC3 Ltd | Professional & scientific | 2019 |
| Dcoa IV Ltd | Real estate | 2024 |
| Dearlove Family Investments Ltd | Real estate | 2025 |
| Debitly Ltd | Information & communication | 2025 |
| Decabbit Ltd | Information & communication | 2013 |
| Deceasays Ltd | Health & social care | 2021 |
| Deedee's Novelties and Collectibles Limited | Wholesale & retail | 2025 |
| Deep Cypher Ltd | Information & communication | 2020 |
| Deimos Space UK Limited | Professional & scientific | 2013 |
| Delta Kappa Ltd | Real estate | 2025 |
| DEN & DEN Travel Ltd | Wholesale & retail | 2005 |
| Denbim Services Limited | Health & social care | 2022 |
| Denboer and Associates Limited | Professional & scientific | 2013 |
| Deniz Courier Ltd | Transport & logistics | 2022 |
| Dennis Trustees Ltd | Other services | 2023 |
| Derant Developments Ltd | Real estate | 2023 |
| Design Integration Limited | Administrative & support | 2005 |
| Designloop Web Ltd | Information & communication | 2024 |
| Diamond Capital Ventures Ltd | Real estate | 2023 |
| Diamond Light Source Limited | Professional & scientific | 2002 |
| Diasorin Limited | Administrative & support | 1986 |
| Dibie Security Connection Limited | Administrative & support | 2018 |
| Didcot Auto Centre Limited | Wholesale & retail | 2026 |
| Didcot Barber Limited | Other services | 2024 |
| Didcot Boxing Academy Ltd | Education | 2021 |
| Didcot Brickwork Ltd | Construction | 2013 |
| Didcot Calor & Paving Centre Limited | Wholesale & retail | 2004 |
| Didcot Design and Prototyping Ltd | Manufacturing | 2022 |
| Didcot Electrical Wholesalers Limited | Wholesale & retail | 2013 |
| Didcot First Limited | Other services | 2007 |
| Didcot Pet Stores Limited | Wholesale & retail | 2019 |
| Didcot Railway Centre Limited | Arts & recreation | 1990 |
| Didcot Subway Ltd | Hospitality | 2019 |
| Didcot Taxis Ltd | Transport & logistics | 2020 |
| Didcot Tyre & Exhaust Limited | Wholesale & retail | 2007 |
| Didcot Tyre Services - DTS Ltd | Wholesale & retail | 2025 |
| Didcot Vaping Ltd | Wholesale & retail | 2018 |
| Didcot Windows Limited | Wholesale & retail | 1991 |
| Digipress.Co Limited | Manufacturing | 2004 |
| Digital Vehicle Technologies Limited | Manufacturing | 2020 |
| Digostics Limited | Manufacturing | 2019 |
| Direct Dispatch Limited | Wholesale & retail | 2020 |
| Discover Consulting Ltd | Professional & scientific | 2018 |
| Dixon Engineering (Air Conditioning) Limited | Energy | 1994 |
| DJR Space Ltd | Manufacturing | 2023 |
| DK House 2 Ltd | Other services | 2025 |
| DK House Ltd | Other services | 2025 |
| Dmjb Products Ltd | Wholesale & retail | 2023 |
| DOE Estates Ltd | Real estate | 2023 |
| Doma Property Ltd | Real estate | 2025 |
| Domestic Appliance Repairs Oxon Ltd | Wholesale & retail | 2019 |
| Dorandi Ltd | Construction | 2015 |