| CJ Coaches Limited | Extraterritorial | 2013 |
| CJS Electrical Services Ltd | Construction | 2020 |
| CJT Properties Ltd | Real estate | 2020 |
| CJV NDT Services Ltd | Administrative & support | 2008 |
| CKP Estates Limited | Real estate | 2022 |
| Clare James Project Associates Ltd | Construction | 2008 |
| Clarke Macaskill Property Group Ltd | Real estate | 2026 |
| Classic Windows (NE) Limited | Construction | 2000 |
| Clayton Glass Limited | Manufacturing | 2004 |
| Clean-Tec North East Ltd | Administrative & support | 2025 |
| Cleanstay Laundrette Durham Limited | Other services | 2026 |
| Clearmid Limited | Hospitality | 1989 |
| Clearwater Instruments Limited | Wholesale & retail | 2008 |
| CLOVER360 Ltd | Professional & scientific | 2023 |
| Cmcltd Limited | Wholesale & retail | 2023 |
| Cmyj Ltd | Real estate | 2019 |
| Coach and Horses PUB Ltd | Hospitality | 2021 |
| Codematik Limited | Information & communication | 2022 |
| Cokain Developments Ltd | Construction | 2003 |
| Commercial Cleaning Solutions (North East) Limited | Administrative & support | 2024 |
| Compare NOW UK Limited | Information & communication | 2022 |
| Complete Material Handling Limited | Administrative & support | 2015 |
| CON Mech Engineers Limited | Manufacturing | 1960 |
| Concept IT Facilities Limited | Information & communication | 2006 |
| Concept IT Services Ltd | Information & communication | 2005 |
| Concept Technology Group Ltd | Financial services | 2024 |
| CONNAX100 Holdings Ltd | Financial services | 2024 |
| Connect Multi-Academy Trust | Education | 2010 |
| Consett AFC Ltd | Arts & recreation | 2013 |
| Construction CMS Limited | Construction | 2007 |
| Contract Services Wood Machinery Ltd | Manufacturing | 2012 |
| Coppy Farm Contractors Limited | Agriculture & fishing | 2019 |
| Corespec Ltd | Manufacturing | 1998 |
| Corinthia Investments 1 Limited | Real estate | 2025 |
| Corinthia Real Estate Limited | Real estate | 2023 |
| Coronation Chippy Limited | Hospitality | 2025 |
| Cotton Socks Photography Ltd | Professional & scientific | 2022 |
| County Durham Arts in Education Agency | Education | 2000 |
| County Durham Engineering and Manufacturing Network Limited | Other services | 2015 |
| County Durham Landscaping Ltd | Professional & scientific | 2026 |
| County Electrical and Property Management Limited | Construction | 2015 |
| Cowie Financial Services Ltd | Professional & scientific | 2017 |
| CPD (North East) Limited | Real estate | 2021 |
| CPO Payroll Ltd | Professional & scientific | 2026 |
| CPT Solutions Ltd | Administrative & support | 2020 |
| Craghead Development Trust Limited | Education | 2004 |
| Create Create Limited | Wholesale & retail | 2019 |
| Creative Decorating North East Ltd | Construction | 2025 |
| Crescer Limited | Real estate | 2020 |
| Croft Travel Limited | Wholesale & retail | 2014 |
| Crosseve 1 Limited | Construction | 2025 |
| Crossroads Languages Limited | Education | 2009 |
| Crucial Limited | Construction | 2024 |
| Cruze Fightwear Ltd | Wholesale & retail | 2022 |
| CRW Professional Services Ltd | Information & communication | 2015 |
| CS Plumbing NE Limited | Construction | 2025 |
| CSU Ltd | Information & communication | 2016 |
| CTC GEO Ltd | Mining & quarrying | 2005 |
| Ctrl - X Digital Limited | Professional & scientific | 2010 |
| Cummings Contractors Limited | Construction | 2015 |
| Curaradi Limited | Extraterritorial | 2025 |
| Customfit Golf Limited | Wholesale & retail | 2010 |
| Cutting Edge Tree Surgery and Fencing Limited | Agriculture & fishing | 2017 |
| CW Heating Services Ltd | Construction | 2015 |
| CW Property Renovations Ltd | Construction | 2025 |
| CW Utilities (North) Limited | Construction | 2024 |
| D & H Property Investments Ltd | Other services | 2021 |
| D & L Motors Ltd | Wholesale & retail | 2026 |
| D D Electrical Contractors Ltd | Construction | 2011 |
| D Davison Building Limited | Construction | 2021 |
| D E Pearce Holdings Ltd | Real estate | 2025 |
| D J Autogas 4X4 Limited | Wholesale & retail | 1996 |
| D L Electricals Ltd | Construction | 2014 |
| D Middleton Energy Services Ltd | Construction | 2018 |
| D Routledge Plumbing Contractors Ltd | Construction | 2019 |
| D&R Property Solutions Ltd | Households | 2020 |
| D.J.S Logistic Solutions Ltd | Professional & scientific | 2019 |
| Dad’S Fish and Chips Limited | Hospitality | 2025 |
| Daleside MOT Limited | Wholesale & retail | 2004 |
| Dannyland Ltd | Administrative & support | 2019 |
| David J Pipes Groundworks Limited | Construction | 2010 |
| Davidson Transport & Distribution Ltd | Transport & logistics | 2025 |
| Debbie & Co Hair & Beauty Limited | Other services | 2025 |
| Delilah Car Sales Limited | Wholesale & retail | 2026 |
| Dent Properties NE Ltd | Real estate | 2023 |
| Derwent Garden Apartment Managemt Company Ltd | Households | 2021 |
| Derwentside Glass (NE) Ltd | Construction | 2017 |
| Deseyer More Limited | Wholesale & retail | 2025 |
| Design Perfect Ltd | Information & communication | 2010 |
| DG Strategic Holdings Ltd | Financial services | 2026 |
| DGD North East Ltd | Manufacturing | 2022 |
| DH1 Travel Ltd | Transport & logistics | 2025 |
| DH9 Design & Marketing Limited | Professional & scientific | 2013 |
| DHK9 Ltd | Agriculture & fishing | 2024 |
| Diamondpropertysolutionsne Limited | Construction | 2025 |
| Digital Cat Consultancy Ltd | Professional & scientific | 2019 |
| Dipta Limited | Real estate | 2015 |
| Direct Submit Internet Services Limited | Information & communication | 2006 |
| Direct Submit Limited | Information & communication | 2006 |
| Dixon Commercial Exports Ltd | Wholesale & retail | 2015 |