- Cassling
- Castle Hills Self Storage
- Castle Resorts and Hotels
- Castle Rock Adventist Hospital
- Castle Worldwide Inc
- Catalina Foothills School District
- Catalyst Events
- Catawba Valley Medical Center
- Caterpillar
- Cathedral of Madeleine
- Cathedral of St. John the Divine
- Cathedral Residences
- Catholic Charities Archdiocese of Galveston-Houston
- Catholic Charities Archdiocese of New York
- Catholic Charities of California
- Catholic Charities of the Diocese of Pittsburgh, Inc.
- Catholic Charities USA
- Catholic Charities, Medical Care Community Partnership
- Catholic Community Services of Southern Arizona, Inc.
- Catholic Diocese of Buffalo
- Catholic Diocese of Sacramento
- Catholic Health Association of the United States
- Catholic Health Association of the United States
- Catholic Health System
- Catholic Healthcare West
- Catholic Medical Center
- Catholic Social Services
- Cathy's Critter Care
- Cathy's Eye Care
- Catskill Regional Medical Center
- Cattaraugus County
- Causemedia, Inc.
- Cauthome Paper Company, Inc.
- Cavanaugh Promotions
- Cavco Industries
- Cayuga Medical Center
- CBIA
- CBM
- CC Myers Inc.
- CCCS of WNC, Inc.
- CCRC Actuaries, LLC
- CCRI
- CCS Fund Raising
- CCSSO
- CDAT Certified Information
- CDC National Institute for Occupational Safety and Health
- CDCLOMH
- Cdi Corp.
- CDM Smith
- CDO Technologies