| K-R-I-T Motor Car Company | business | Detroit | 1909 |
| Kaiser Jeep | business, automobile manufacturer | Toledo | 1953 |
| Kaiser Motors | automobile manufacturer | Ypsilanti | 1945 |
| Kaiser Permanente | nonprofit organization, hospital network, business, private healthcare | Oakland | 1945 |
| Kalem Company | film production company | New York City | 1907 |
| Kaltura | software company, business | New York, New York City | 2006 |
| Kaman Corporation | public company, aerospace manufacturer | Bloomfield, Connecticut | 1945 |
| Kansas State University | public educational institution of the United States, land-grant university, public university | — | 1863 |
| Kaplan International Languages | business, enterprise | London | 1967 |
| Katz's Delicatessen | restaurant | — | 1888 |
| Kayak.com | travel website, business | Stamford | 2004 |
| Kaypro | business | San Diego | 1981 |
| Kelvinator | business | — | 1914 |
| Keurig Dr Pepper | business, enterprise, public company | Burlington | 2018 |
| KeyBank | bank, business, financial institution, enterprise, credit institution, public company | Cleveland | 1825 |
| Keystone Studios | business | Edendale | 1912 |
| 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 |
| KLA Corporation | business, public company | Milpitas | 1997 |
| 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 |
| Kohler Company | business, enterprise | Kohler | December 6, 1873 |
| Kongregate | video game publisher, website | San Francisco | 2006 |
| Kraft Foods Inc. | public company | Northfield | 1923 |
| Kraft Heinz | organization, business, enterprise, public company | Pittsburgh | 2015 |
| Kraken | bitcoin exchange, cryptocurrency exchange | San Francisco | 2011 |
| Krispy Kreme | fast food restaurant chain, restaurant chain, public company | Winston-Salem | July 13, 1937 |
| Krystal | fast food restaurant chain | Atlanta | 1932 |
| Kylie Cosmetics | website, brand, business | Oxnard | 2014 |