| C. F. Martin & Company | business | Nazareth | 1833 |
| C. H. Robinson Worldwide | business, public company | Eden Prairie | 1905 |
| Cabot Corporation | business, public company | Boston | 1882 |
| CACI | corporation, public company | Arlington County | July 17, 1962 |
| Cadence Design Systems | organization, business, enterprise, public company | San Jose | 1988 |
| Calico | business | San Francisco | September 18, 2013 |
| California Academy of Sciences | planetarium, nonprofit organization, natural history museum, public aquarium, academy of sciences, learned society | San Francisco | 1853 |
| California College of the Arts | private not-for-profit educational institution, art academy, university | Oakland, San Francisco | 1907 |
| California Institute of the Arts | private not-for-profit educational institution, film school, art academy, private university | — | 1961 |
| California Pizza Kitchen | restaurant chain, pizzeria chain, public company | Los Angeles | 1985 |
| California State University | state university system, university | Long Beach | 1857 |
| California State University, Bakersfield | public educational institution of the United States, university | Bakersfield | 1965 |
| California State University, East Bay | public educational institution of the United States, university | Hayward | 1957 |
| California State University, Fresno | public educational institution of the United States, university | Fresno | 1911 |
| California State University, Northridge | public educational institution of the United States, public university | Los Angeles | 1958 |
| California State University, San Bernardino | public educational institution of the United States, university, Hispanic-serving institution | San Bernardino | 1965 |
| Calvin University | church college, private not-for-profit educational institution, university | East Grand Rapids | 1876 |
| Cambridge Analytica | business, enterprise | London | 2014 |
| Cambridge University Press | book publisher, open-access publisher, university press, academic publisher | Cambridge | 1534 |
| Cannondale Bicycle Corporation | bicycle manufacturer, brand, business | Bethel | 1971 |
| Canoo | business, automobile manufacturer, public company | Torrance | 2017 |
| Cape Air | airline | Hyannis | 1989 |
| Capital One | business, enterprise, credit institution, public company | McLean | 1994 |
| Cardinal Health | business, medical device company, enterprise, public company | Dublin | 1971 |
| Carleton College | liberal arts college, private not-for-profit educational institution | Northfield | 1866 |
| CarMax | business, public company | Goochland County | 1993 |
| Carnegie Mellon University | research university, private not-for-profit educational institution, private university | Pittsburgh | 1900 |
| Carnegie Steel Company | enterprise | Pittsburgh | 1892 |
| Carrier Corporation | business, public company | Farmington | June 26, 1915 |
| Carroll Shelby International | automobile manufacturer | Enterprise | August 17, 1962 |
| Cartercar | business, automobile manufacturer | Pontiac | 1905 |
| Case Corporation | brand, business | United States | 1842 |
| Case IH | brand, business, tractor brand | Racine | 1984 |
| Castello di Amorosa | winery | — | April 2007 |
| Castle Rock Entertainment | television production company, film production company | Beverly Hills | June 19, 1985 |
| Caterpillar Inc. | business, enterprise, public company | Irving | 1925 |
| CBS | radio network, television network | CBS Building | September 18, 1927 |
| CBS Films | film production company, film distributor | Los Angeles | March 2007 |
| CBS Radio | business | New York City | 1928 |
| Cecil H. Green Library | academic library, library building | Stanford | 1919 |
| Celanese Corporation | business, public company | Irving | 1999 |
| Celera Corporation | business | Rockville, Alameda | May 1998 |
| Cell Press | imprint, academic publisher | Cambridge | 1986 |
| Centurion Air Cargo | airline | Miami International Airport | 1985 |
| Century 21 Real Estate | estate agent, business, enterprise | Madison | 1971 |
| Cerberus Capital Management | business, enterprise | New York City | 1992 |
| CH2M Hill | former entity, business | Meridian | 1946 |
| Champ Car | sports competition, recurring sporting event, business | — | 1979 |
| Chan Zuckerberg Initiative | limited liability company, organization, enterprise | Redwood City | 2015 |
| Chaosium | tabletop role-playing game publisher, board game publishing company, business | Hayward, Albany | October 31, 1975 |
| Chapman University | private not-for-profit educational institution, university | Orange | 1861 |
| Charlton Comics | business | Derby | 1945 |
| Charter Arms | business | Shelton | 1964 |
| Chateau Marmont | hotel | — | 1927 |
| Chautauqua Airlines | airline | Indianapolis | 1973 |
| Checker Motors Corporation | automobile manufacturer | Kalamazoo | 1922 |
| Chegg | dot-com company, technology company, public company | Santa Clara | 2005 |
| Chemical Bank | business | Midland, New York City | 1954 |
| Chevron Corporation | oil company, corporation, organization, gas station chain, enterprise, public company | — | — |
| Chicago Board of Trade | futures exchange, business | Chicago | 1848 |
| Chicago Mercantile Exchange | futures exchange, business | Chicago | 1898 |
| Chicago The Musical Ambassador Theater | Broadway theatre, theatre building, movie theater | — | February 11, 1921 |
| Chicago, Rock Island and Pacific Railroad | railway company, business, transport company | Chicago | 1866 |
| Chick-fil-A | fast food restaurant chain | Georgia | 1946 |
| Chikara | business, professional wrestling promotion | Philadelphia | 2002 |
| Chili's | restaurant chain | Coppell | March 13, 1975 |
| Chipotle Mexican Grill | restaurant chain, organization, business, enterprise, public company | Denver, Newport Beach | July 13, 1993 |
| Choate Rosemary Hall | boarding school, organization | Wallingford | 1890 |
| Choice Hotels | hotel chain, business, public company | Rockville, Silver Spring | 1939 |
| Christopher Newport University | public educational institution of the United States, university, open-access publisher | — | 1961 |
| Chuck E. Cheese | indoor play space, restaurant chain, pizzeria chain, public company | Irving | May 17, 1977 |
| Church & Dwight | business, enterprise, public company | Ewing Township | 1846 |
| Church's Texas Chicken | fast food restaurant chain, restaurant chain | Sandy Springs | April 17, 1952 |
| Cinemaware | video game publisher, video game developer | Burlingame | 1986 |
| Circle | dot-com company, business | Boston | October 2013 |
| Circuit City Stores | business, enterprise | Richmond | 1984 |
| Circus Circus Las Vegas | casino, hotel | — | October 18, 1968 |
| Cisco | business, enterprise, public company | San Jose | 1984 |
| Citadel LLC | business, unlisted public company, company, financial services | Miami | 1990 |
| Citgo | business, gas station chain | Houston | 1910 |
| Citibank | bank, business, financial institution, credit institution | Sioux Falls, New York City | 1865 |
| Citizens Financial Group | bank, business, public company | Providence | 1954 |
| City College of New York | public educational institution of the United States, higher education institution | New York City | 1847 |
| Clarivate | public company | Philadelphia, London | October 3, 2016 |
| Clark Atlanta University | historically black college or university, private not-for-profit educational institution, private university | — | September 19, 1865 |
| Clark University | liberal arts college, Colleges That Change Lives, private not-for-profit educational institution, private university | Worcester | 1887 |
| Clarkson University | private not-for-profit educational institution, university | — | 1896 |
| CLS Group | business | New York | 2002 |
| ClubJenna | television production company, pornographic film studio | Scottsdale | 2000 |
| Coastal Carolina University | public educational institution of the United States, university | Conway | 1954 |
| CodeGear | business, enterprise | Scotts Valley, California | 2006 |
| Cognex Corporation | business, public company | Natick | 1981 |
| Cold Spring Harbor Laboratory | nonprofit organization, research institute, academic publisher | — | 1890 |
| Cole Haan | business, subsidiary company, brick and mortar | Greenland | 1928 |
| Coleco | brand, business | West Hartford | 1932 |
| College of the Holy Cross | liberal arts college, private not-for-profit educational institution, university | Worcester | 1843 |
| Collins Aerospace | defense contractor, aerospace manufacturer | Charlotte | 2018 |
| Colorado College | liberal arts college, private not-for-profit educational institution | Colorado Springs | 1874 |
| Colorado State University | public educational institution of the United States, land-grant university, public research university | — | 1870 |
| 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 Graduate School of Journalism | graduate school, academic department, journalism school | New York City | 1912 |
| Columbia University Press | book publisher, nonprofit organization, university press | New York City | 1893 |
| Comair | airline, defunct organization, wholly owned subsidiary | Erlanger | 1977 |
| Combustion Engineering | business | Stamford | 1912 |
| Comcast | telecommunications company, business, enterprise, public company | Philadelphia | June 28, 1963 |
| Common Crawl | dot-com company, nonprofit organization | — | 2008 |
| Compaq | technology company, business, enterprise | Houston | February 16, 1982 |
| Compass Airlines | airline | Minneapolis–Saint Paul International Airport | 2006 |
| Conair Corporation | business, enterprise | East Windsor Township | 1959 |
| Concentrix | business | Fremont | 2004 |
| Concord | record company, business | Beverly Hills | 1973 |
| Conexant | business, enterprise | Irvine | 1999 |
| Conrail | railway company | Philadelphia | April 1, 1976 |
| Consol Energy | business, enterprise, public company | Pittsburgh | 1991 |
| Continental Express | airline | Houston | 1986 |
| Continental Micronesia | airline | Tamuning | 1968 |
| Cooper Union | college, private not-for-profit educational institution | — | 1859 |
| Coors Brewing Company | brewery, business | Golden | 1873 |
| Cord Automobile | business | United States | 1929 |
| CoreCivic | business, enterprise, public company | Nashville | 1983 |
| CoreWeave | business, enterprise | Roseland | 2017 |
| CosMc's | fast food restaurant | Chicago | December 7, 2023 |
| Coty | business, enterprise, public company | New York City | 1904 |
| CouchSurfing | hospitality service, website, business | San Francisco | April 2, 2003 |
| 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 |
| Coursera | massive open online course provider, website, education company, public company | Mountain View | 2012 |
| Cracker Barrel | restaurant chain, public company | Lebanon | September 19, 1969 |
| Crackle | business, video streaming service, streaming service | Culver City | July 2007 |
| Cray | public company | Seattle | 1972 |
| CRC Press | book publisher, publishing house | Boca Raton | 1903 |
| Creative Artists Agency | talent agency, company | Century City | 1975 |
| Creative Micro Designs | business | East Longmeadow | 1987 |
| Credo Reference | business | Boston | 1999 |
| CrimethInc. | collective, group of humans, publishing house | — | 1996 |
| Cross Creek Pictures | film production company | Los Angeles | 2009 |
| CrowdStrike | business, public company | Austin | August 29, 2011 |
| Crown Castle International Corp. | organization, real estate investment trust, company, public company | Houston | January 1, 1994 |
| 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 |
| CSX Transportation | railway company | — | July 1, 1986 |
| Culinary Institute of America | private not-for-profit educational institution, cooking school, private university | Hyde Park, New Haven, Hyde Park | May 22, 1946 |
| Currier and Ives | male duo, business | New York City | 1835 |
| Curtis Institute of Music | conservatory, private not-for-profit educational institution, college of music | — | 1924 |
| Cushman & Wakefield | business, enterprise, public company | New York City | 1917 |
| CVS Pharmacy | business, pharmacy chain | Woonsocket | 1963 |
| Cyan Worlds | privately held company, video game developer, business | Wilmington, Mead | 1987 |
| Cypress Semiconductor | business | San Jose | 1982 |
| Cyrix | business, public company | Richardson | 1988 |