| Clarity Telecom | South Dublin County Council |
| Clear Mobile | |
| Clearwood | |
| CleverCards | |
| Click Media | Dún Laoghaire-Rathdown County Council |
| Cloud Mechanix | |
| Cloud90 | |
| Cloudcards Ltd | |
| CloudCIX Ltd | Cork City Council |
| CluneTech | |
| Cluster | |
| Cobweb Design & Marketing | Dublin City Council |
| CoCreate | |
| Code Institute | Dublin City Council |
| Codec | Dublin City Council |
| Coded Web Design | |
| CodeEast Digital Systems Ltd | |
| Cognition World | |
| Combined Media | Dublin City Council |
| Comeragh Controls | Tipperary County Council |
| CommerceGate Ireland Ltd | Dublin City Council |
| Commission for Communications Regulation | Dublin City Council |
| Communicraft | Dublin City Council |
| CompuCal Calibration Solutions | |
| Compupac I.T. Solutions Ltd | Donegal County Council |
| Compuspeak | |
| ComputerJobs.ie | Dún Laoghaire-Rathdown County Council |
| ComTech | |
| Connect Electronics Ltd | Dublin City Council |
| Connect.ie | Dublin City Council |
| Construction IT Alliance Ltd | Dublin City Council |
| Continuous Ventures | |
| Continuum | Dublin City Council |
| Control and Information Management (CIM) Ltd | Dublin City Council |
| ControlDTx | |
| CoolPlanet Ltd | |
| CoolPlanet Ltd | |
| Cora Systems | Leitrim County Council |
| Corballis Technologies | |
| Core Communications | Kildare County Council |
| Cork Electronics Industry Association | Cork City Council |
| Cork Insitute of Technology | Cork City Council |
| CorkBIC | |
| Corlytics | |
| Corporate Governance Institute | |
| Corteza | |
| Cosmo Pharmaceuticals | Dublin City Council |
| CourseCo | |
| Coworking.ie | |
| CR2 | Dublin City Council |