| CircuitVision | Florida |
| CircuitWerkes, Inc. | Florida |
| Circul8.me | |
| Circular Genomics, Inc. | New Mexico |
| Circular Systems | California |
| CircularEdge | New Jersey |
| Circulate Health | |
| CirculaTech | |
| Circulent, LLC | Connecticut |
| Circulogene | Florida |
| Circumvent Pharmaceuticals, Inc. | Oregon |
| Circurna ciRNA Technology | |
| Cirexx Corporation | California |
| Ciright, Inc. | Pennsylvania |
| Cirius Therapeutics, Inc. | |
| Cirkadia, Inc. | Maine |
| Cirkuit Commerce | Indiana |
| Cirkuit Networks, Inc. | Indiana |
| Ciro Vargas Clemow | |
| CirqPlus | Arizona |
| Cirque Corporation | Utah |
| Cirra Networks | Texas |
| Cirrascale Cloud Services, LLC | California |
| Cirries | Texas |
| Cirris Systems Corporation | Utah |
| Cirrus Business Consulting, LLC | |
| Cirrus Insight | California |
| Cirrus Logic, Inc. | Texas |
| Cirrus Medical Network, Inc. | |
| Cirrus Secure | Colorado |
| Cirrus Sky Technology Park | Wyoming |
| Cirrus Streaming | Florida |
| Cirrus Systems | Alabama |
| Cirrus Therapeutics | |
| CirrusLab, Inc. | |
| CirrusMD | |
| Cirsium Biosciences | |
| Cirtec Medical | Minnesota |
| Cirtru Classifieds, Inc. | |
| Cirv, Inc. | Washington |
| CIS Internet | West Virginia |
| CIS Recruiters | New Jersey |
| CIS Technical Services, Inc. | New Hampshire |
| Cisco College | Texas |
| Cisco Investments | California |
| Cisco Networking Academy | California |
| Cisco Systems, Inc. | California |
| Cisco Talos Intelligence Group | |
| CisCom Solutions | Kentucky |
| Cision | Illinois |