| ConocoPhillips | business, enterprise, public company | Houston | 1875 |
| Conrail | railway company | Philadelphia | April 1, 1976 |
| Consol Energy | business, enterprise, public company | Pittsburgh | 1991 |
| Constellation Brands | business, company, public company | Victor | 1945 |
| Continental Airlines | airline | Chicago, Denver, Houston, El Paso, Los Angeles | 1934 |
| Continental Express | airline | Houston | 1986 |
| Convair | launch service provider, aerospace manufacturer | San Diego | 1943 |
| Cooper Tire & Rubber Company | business, enterprise, public company | Findlay | 1926 |
| Cooper Union | college, private not-for-profit educational institution | — | 1859 |
| Coors Brewing Company | brewery, business | Golden | 1873 |
| Cornell University | research university, private not-for-profit educational institution, land-grant university, sun grant institution, private university | Ithaca | 1865 |
| Cornell University Press | book publisher, university press | Ithaca | 1869 |
| Corning Inc. | organization, business, enterprise, public company | Corning | 1851 |
| Corteva | business, public company | Washington, D.C. | March 15, 2018 |
| Cosmopolitan of Las Vegas | casino, hotel | — | April 2004 |
| Costco | business, retail chain, enterprise, public company | Issaquah | 1983 |
| Coty | business, enterprise, public company | New York City | 1904 |
| CouchSurfing | hospitality service, website, business | San Francisco | April 2, 2003 |
| Courant Institute School of Mathematics, Computing, and Data Science | academic institute, faculty, higher education institution, organization | — | 1935 |
| Coursera | massive open online course provider, website, education company, public company | Mountain View | 2012 |
| Courtyard by Marriott | hotel chain | Bethesda | 1983 |
| CoverGirl | brand, business | Maryland | 1961 |
| Cox Enterprises | enterprise | Atlanta | 1898 |
| Crave Entertainment | video game developer | Newport Beach | 1997 |
| Cray | public company | Seattle | 1972 |
| Crayola LLC | business, enterprise | Forks Township | 1885 |
| Creative Commons | nonprofit organization, publishing house, author | Mountain View | January 15, 2001 |
| Creative Micro Designs | business | East Longmeadow | 1987 |
| Credo Reference | business | Boston | 1999 |
| Cricket Wireless | mobile virtual network operator, telecommunications company, business, mobile phone store chain | San Diego | 1999 |
| CrimethInc. | collective, group of humans, publishing house | — | 1996 |
| Crocs, Inc. | retail chain, brick and mortar, public company | Longmont | 2002 |
| Crosley | business, automobile manufacturer | Cincinnati | 1937 |
| CrossFit | hobby, business | Santa Cruz | 2000 |
| Crown Castle International Corp. | organization, real estate investment trust, company, public company | Houston | January 1, 1994 |
| Cruise/Wagner Productions | film production company | Los Angeles | July 1992 |
| Crumbl Cookies | restaurant chain | Lindon | 2017 |
| Crunchbase | data set, website, business, online database | San Francisco | July 2007 |
| Crunchyroll | application software, video streaming service, Internet audio-visual programming service provider, mobile app, streaming service, Internet television | San Francisco | May 14, 2006 |
| Cryptic Studios | video game developer | Los Gatos | June 2000 |
| Crystal Dynamics | video game developer | Redwood City | 1992 |
| CSX Corporation | organization, business, enterprise, public company | CSX Transportation Building | November 1, 1980 |
| Culinary Institute of America | private not-for-profit educational institution, cooking school, private university | Hyde Park, New Haven, Hyde Park | May 22, 1946 |
| Cummins | business, public company | Columbus | 1919 |
| CUNY Graduate School and University Center | graduate school, public educational institution of the United States, research institute, open-access publisher | New York City | 1961 |
| Currier and Ives | male duo, business | New York City | 1835 |
| Curtiss-Wright | holding company, business, public company, aerospace manufacturer | Charlotte | 1929 |
| CVS Health | organization, business, enterprise, public company | Rhode Island, Woonsocket | 1963 |