| Columbia College | college | — | 1754 |
| Columbia Pictures | film production company, film distributor | United States, Culver City | 1918 |
| Columbia Sportswear Company | business, enterprise, brick and mortar, public company | Cedar Mill | 1938 |
| Columbia University Press | book publisher, nonprofit organization, university press | New York City | 1893 |
| Columbia University Vagelos College of Physicians and Surgeons | graduate school, university, medical school | New York City | 1767 |
| Comcast | telecommunications company, business, enterprise, public company | Philadelphia | June 28, 1963 |
| Comerica | bank, business, financial institution, credit institution, public company | Dallas | 1849 |
| Commonwealth Fusion Systems | business | Devens | 2018 |
| CommScope | business, public company | Claremont | 1976 |
| Comodo Group | business, enterprise | Clifton | 1998 |
| Comscore | website, business, public company | Reston | 1999 |
| Concentrix | business | Fremont | 2004 |
| Condé Nast | publishing house | One World Trade Center | 1909 |
| Conoco | oil company, defunct organization | Houston | 1875 |
| Conrail | railway company | Philadelphia | April 1, 1976 |
| Constellation Energy | public company | Baltimore | 1999 |
| Continental Micronesia | airline | Tamuning | 1968 |
| Control Data Corporation | business, enterprise | Bloomington | 1957 |
| Converse | brand, business | Boston | 1910 |
| Cord Automobile | business | United States | 1929 |
| CoreWeave | business, enterprise | Roseland | 2017 |
| Cornell Law School | law school | — | 1887 |
| Cornell University | research university, private not-for-profit educational institution, land-grant university, sun grant institution, private university | Ithaca | 1865 |
| 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 |
| Council on Vertical Urbanism | publishing house, organization | Illinois Institute of Technology | 1969 |
| Courant Institute School of Mathematics, Computing, and Data Science | academic institute, faculty, higher education institution, organization | — | 1935 |
| CoverGirl | brand, business | Maryland | 1961 |
| Cox Communications | internet service provider, business | Phoenix | 1962 |
| Cox Enterprises | enterprise | Atlanta | 1898 |
| Cracker Barrel | restaurant chain, public company | Lebanon | September 19, 1969 |
| Crave Entertainment | video game developer | Newport Beach | 1997 |
| Cray | public company | Seattle | 1972 |
| Crayola LLC | business, enterprise | Forks Township | 1885 |
| Creative Artists Agency | talent agency, company | Century City | 1975 |
| Creative Commons | nonprofit organization, publishing house, author | Mountain View | January 15, 2001 |
| Creighton University | private not-for-profit educational institution, university, open-access publisher | Omaha | 1878 |
| Crocs, Inc. | retail chain, brick and mortar, public company | Longmont | 2002 |
| Crosley | business, automobile manufacturer | Cincinnati | 1937 |
| CrossFit | hobby, business | Santa Cruz | 2000 |
| CrowdStrike | business, public company | Austin | August 29, 2011 |
| 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 Cruises | business, cruise line | Los Angeles | 1988 |
| Culligan | business | Rosemont | 1936 |