| Kirby Company | Cleveland | 1914 |
| Kmart | Detroit | 1962 |
| Knoll | East Greenville | 1938 |
| Koch, Inc. | Wichita | 1940 |
| Kodak | Rochester, New York City | 1882 |
| Kohlberg Kravis Roberts | New York City | 1976 |
| Kohler Company | Kohler | December 6, 1873 |
| Koss Corporation | Milwaukee | 1953 |
| Kroger | Cincinnati | 1882 |
| L3Harris Technologies | Melbourne | June 29, 2019 |
| La Senza | Montreal | 1990 |
| La-Z-Boy | Monroe | 1927 |
| Landmark Worldwide | San Francisco | 1991 |
| Language Creation Society | Garden Grove | 2007 |
| Las Vegas Sands | Las Vegas, Paradise | 1937 |
| Lazard | New York City | July 12, 1848 |
| LeCroy Corporation | Chestnut Ridge | 1964 |
| Lehman Brothers | New York City | 1850 |
| LenovoEMC | San Diego | 1980 |
| Level 3 Communications | Frankfurt | 1985 |
| Levi Strauss & Co. | San Francisco, Levi's Plaza | 1853 |
| Lexicon | Woodbury | 1971 |
| Lexmark | Lexington | March 27, 1991 |
| Lime | San Mateo | January 2017 |
| Line 6 | Calabasas | 1996 |
| Lionbridge | Waltham | 1996 |
| Litton Industries | Milwaukee | 1953 |
| Loews Corporation | New York City | 1946 |
| Logitech | Lausanne, Newark | October 2, 1981 |
| Lollapalooza | — | 1991 |
| Lotus Software | Cambridge | 1982 |
| Lycoming | Williamsport | 1845 |
| M&T Bank | Buffalo | 1856 |
| Mack Trucks | Allentown, Greensboro | 1900 |
| Macromedia | San Francisco | February 25, 1992 |
| Macy's, Inc. | Cincinnati, Macy's Herald Square | 1929 |
| Magpul | — | — |
| MakerBot Industries | New York City | January 20, 2009 |
| Marathon Oil | Houston | 1887 |
| Marathon Petroleum | Findlay | 2009 |
| Marmon Motor Car Company | Indianapolis | 1902 |
| Marmot | Santa Rosa | 1974 |
| Masdar | Abu Dhabi | April 2006 |
| Masten Space Systems | Mojave | 2004 |
| Match Group | Kerrville | 2009 |
| McGraw-Hill Education | New York City | 1888 |
| McIntosh Laboratory | Binghamton, New York City | 1949 |
| McKesson Corporation | Irving | 1994 |