| Contactsector Limited | Construction | 1987 |
| Cooden Consultants Limited | Professional & scientific | 2020 |
| Coolertech Limited | Manufacturing | 2012 |
| Coolhurst Containers Ltd | Construction | 2023 |
| Coolhurst Property Ltd | Real estate | 2023 |
| Coopers Green Homes Limited | Real estate | 2019 |
| Coppard Giles Limited | Professional & scientific | 2003 |
| Coppercrest Developments Limited | Real estate | 1988 |
| Coppercrest Estates Limited | Real estate | 1987 |
| Copping Consulting Ltd | Professional & scientific | 2018 |
| Cops Docs Limited | Professional & scientific | 1995 |
| Copypop Limited | Professional & scientific | 2020 |
| Cornelia James Ltd | Manufacturing | 1946 |
| Cornstone Consulting Limited | Professional & scientific | 2014 |
| Corporate Records Limited | Information & communication | 2009 |
| Corvus Folk CIC | Arts & recreation | 2025 |
| Cosmic-Careers Limited | Administrative & support | 2023 |
| Countryside Carpentry & Construction Ltd | Construction | 2026 |
| County Game Farms Limited | Agriculture & fishing | 2003 |
| Courtin and Warner Limited | Manufacturing | 1950 |
| Courtney Commercial Limited | Professional & scientific | 2001 |
| Courtyard Keys Limited | Wholesale & retail | 2003 |
| Courtyard Residents Association Limited(The) | Real estate | 1986 |
| Courtyard Shoe Repairs Limited | Other services | 2003 |
| Covent Garden Gallery Limited | Wholesale & retail | 1975 |
| Coverpoint Limited | Professional & scientific | 2014 |
| CP Atkins Property's Ltd | Real estate | 2022 |
| Cpel Limited | Professional & scientific | 2010 |
| Crabapple Cottage B&B Ltd | Hospitality | 2022 |
| Crafted in Lewes Ltd | Manufacturing | 2017 |
| Craigasmith Limited | Professional & scientific | 2019 |
| Creat-Ed Consulting Limited | Education | 2023 |
| Created by Will Ltd | Professional & scientific | 2024 |
| Creative Education (Training) Limited | Education | 2009 |
| Creative Interactive Limited | Information & communication | 2008 |
| Creative Promotions and Events Ltd | Professional & scientific | 2021 |
| Creative Return Ltd | Construction | 2024 |
| Creative Utopia Limited | Education | 2017 |
| Credit & Financial Risk Limited | Financial services | 1986 |
| Creed Limited | Education | 1991 |
| Crimpit LLC | | 2023 |
| Croghan Pictures Limited | Information & communication | 2022 |
| Cromwell Place (Lewes) Freehold Company Limited | Households | 2009 |
| Cross Commercial Developments Ltd | Construction | 2018 |
| Cross Construction (Sussex) Limited | Construction | 2001 |
| Cross Developments (Sussex) Limited | Construction | 2015 |
| Cross Homes (Sussex) Limited | Construction | 2014 |
| Cross Homes Lewes Ltd | Construction | 2020 |
| Cross HQ Developments Ltd | Construction | 2018 |
| Crosshaven Management Limited | Households | 2013 |
| Crowbrook Ltd | Professional & scientific | 2010 |
| Crown Events Limited | Arts & recreation | 2007 |
| Crown Publishing Limited | Manufacturing | 2022 |
| CRU Construction Limited | Construction | 2006 |
| Crumble and Core Ltd | Arts & recreation | 2017 |
| Cryoletters LLP | | 2003 |
| Csoy Management Limited | Professional & scientific | 2012 |
| Cucumber Productions Limited | Information & communication | 2013 |
| Cuilfail Estate Limited | Households | 1993 |
| Curry Cottage Offham Limited | Hospitality | 2023 |
| Customer Connect Ltd | Wholesale & retail | 2021 |
| Customer Service of the Year Limited | Professional & scientific | 2012 |
| CUT 'N' Edge Solid Surface Ltd | Manufacturing | 2020 |
| Cut'N'Edge Joinery Limited | Manufacturing | 2016 |
| Cutesy Bundles Limited | Wholesale & retail | 2024 |
| Cutting Edge CNC Ltd | Manufacturing | 2013 |
| Cwcw Studio Limited | Arts & recreation | 2024 |
| D Rayner Ltd | Construction | 2004 |
| D S Decor (South East) Limited | Administrative & support | 2003 |
| D.E.H. Electrical Contractors Limited | Construction | 2010 |
| D.F. Tourle Ltd. | Construction | 1995 |
| D16 Consulting Limited | Information & communication | 2016 |
| DAF Risk Consulting Limited | Construction | 2013 |
| Dagobah Systems Limited | Information & communication | 1998 |
| Daitasol Ltd | Administrative & support | 2026 |
| Dakin Electrical Services Ltd | Construction | 2013 |
| Dame Vera Lynn Children's Charity | Administrative & support | 2001 |
| Dance Sussex Limited | Arts & recreation | 2019 |
| Dandee Ltd | Wholesale & retail | 2024 |
| Danger Mouse Properties LLP | | 2009 |
| Darcy Clothing Limited | Wholesale & retail | 2010 |
| Dark Skies Theatre Ltd | Arts & recreation | 2019 |
| Darling Hydro Ltd | Professional & scientific | 2024 |
| Dart Vale Boarding Cattery Limited | Administrative & support | 2003 |
| Dash Consulting Limited | Information & communication | 2013 |
| David Campion Limited | Administrative & support | 2010 |
| David J Bennett Limited | Professional & scientific | 2014 |
| David Mack Ceramics Ltd | Manufacturing | 2022 |
| David Savage Setting OUT Ltd | Professional & scientific | 2014 |
| Dawson Denim Ltd | Manufacturing | 2018 |
| Daybreak Holdings Ltd | Education | 2015 |
| DCR Wheels Ltd | Wholesale & retail | 2017 |
| DE Warenne Holdings Ltd | Financial services | 2021 |
| Deans Farm Estate Ltd | Agriculture & fishing | 2017 |
| Decibels Audio Ltd | Wholesale & retail | 2022 |
| Deck Chair Digital Limited | Information & communication | 2016 |
| Decking & Felting Limited | Construction | 1971 |
| DEE Sheehan Limited | Arts & recreation | 2002 |
| Deegee Media London Limited | Information & communication | 2019 |
| Deep Dive Data Services Ltd | Information & communication | 2025 |