| K-Swiss | business, subsidiary company | Westlake Village | 1966 |
| Kaggle | website, business, data science competition platform | San Francisco | April 2010 |
| Kahr Arms | business | Pike County | 1995 |
| Kaiser Jeep | business, automobile manufacturer | Toledo | 1953 |
| Kaiser Permanente | nonprofit organization, hospital network, business, private healthcare | Oakland | 1945 |
| Kalitta Air | airline | Ypsilanti | 2000 |
| Kaltura | software company, business | New York, New York City | 2006 |
| Kansas City Southern Railway | railway company | Kansas City | 1887 |
| Kansas State University | public educational institution of the United States, land-grant university, public university | — | 1863 |
| Kaplan International Languages | business, enterprise | London | 1967 |
| Kayak.com | travel website, business | Stamford | 2004 |
| KBR, Inc. | private military company, public company | Houston | 1998 |
| Keds | business, subsidiary company | Rockford | 1916 |
| Kellanova | business, enterprise, public company | Chicago | February 19, 1906 |
| Kelvinator | business | — | 1914 |
| Kent State University | public educational institution of the United States, public research university | Kent | 1910 |
| Kentucky State University | historically black college or university, public educational institution of the United States, land-grant university, public university | — | 1886 |
| KeyBank | bank, business, financial institution, enterprise, credit institution, public company | Cleveland | 1825 |
| King Features Syndicate | animation studio, book publisher, news agency, publishing house, print syndicate | New York City | 1915 |
| Kings Island | amusement park | — | 1972 |
| Kingston Technology | business, enterprise | Fountain Valley | 1987 |
| Kirby Company | business | Cleveland | 1914 |
| KLA Corporation | business, public company | Milpitas | 1997 |
| Klasky Csupo | animation studio | Los Angeles | 1982 |
| Knight's Armament Company | business, enterprise | Titusville | 1983 |
| Knoll | business, subsidiary company, enterprise, public company | East Greenville | 1938 |
| Koch, Inc. | privately held company, business, enterprise | Wichita | 1940 |
| Kodak | camera manufacturer, holding company, business, enterprise, public company | Rochester, New York City | 1882 |
| Kodansha USA Publishing, LLC | comics publishing company, publishing house | New York City | July 1, 2008 |
| Kohl's | department store chain, business, public company | Menomonee Falls | 1962 |
| Kohlberg Kravis Roberts | investment company, financial services company, asset management company, business, private equity firm | New York City | 1976 |
| Kohn Pedersen Fox | architectural firm | Salmon Tower Building | 1976 |
| Kongregate | video game publisher, website | San Francisco | 2006 |
| Kraft Heinz | organization, business, enterprise, public company | Pittsburgh | 2015 |
| Kumon | supplementary educational institution for children, business, enterprise | Osaka | 1958 |