| Uber | food delivery, platform company, Internet booking engine, ridesharing company, organization, business, data controller, online taxi service, enterprise, software, public company | San Francisco | March 2009 |
| Ubiquiti | business, enterprise, public company | New York City | October 2003 |
| Udemy | website, education company | San Francisco | 2010 |
| UL LLC | standards organization, certification services provider, partnership | Northbrook | 1894 |
| Ulta Beauty | business, retail chain, public company | Bolingbrook | 1990 |
| Ultimate Pro Wrestling | business | California | 1998 |
| Undead Labs | business | Seattle | November 23, 2009 |
| Under Armour | business, enterprise, public company | Baltimore | 1996 |
| Unimation | business | — | 1962 |
| Union College | private not-for-profit educational institution, private university | Schenectady | February 25, 1795 |
| Union Iron Works | business | San Francisco | 1849 |
| United Airlines | holding company, airline, public company | Chicago, Willis Tower | April 6, 1926 |
| United Airlines Holdings | business, enterprise, public company | Chicago | December 30, 1968 |
| United Express | brand, airline | Chicago | 1985 |
| United Launch Alliance | launch service provider, privately held company | Centennial | December 1, 2006 |
| United Natural Foods | business, public company | Providence | 1996 |
| United Plankton Pictures | privately held company | Burbank | April 1, 1998 |
| United Space Alliance | business, enterprise | Houston | August 1995 |
| United States Army Command and General Staff College | staff college | Fort Leavenworth | 1881 |
| United States Army Infantry School | military infantry school | Fort Benning | 1918 |
| United States Army War College | Direct Reporting Unit, staff college, military school | — | 1901 |
| United States Centers for Disease Control and Prevention | United States federal agency, open-access publisher | Atlanta | — |
| United States Military Academy | Direct Reporting Unit, public educational institution of the United States, military museum, military academy | — | March 16, 1802 |
| United States National Library of Medicine | national library, medical library | Bethesda | 1836 |
| United States Navy Strike Fighter Tactics Instructor program | military school | — | March 3, 1969 |
| United States Playing Card Company | publishing house, business | Erlanger | 1867 |
| United States Rubber Company | business | Naugatuck | 1892 |
| United States Wrestling Association | business | Memphis | 1989 |
| United Technologies Corporation | business, enterprise, public company | Hartford | 1929 |
| Universal Animation Studios | television production company, animation studio | Universal City, Glendale | 1991 |
| Universal Content Productions | television production company | Universal City | June 1, 2008 |
| Universal Studios Home Entertainment | media distributor | Universal City | 1979 |
| University of Alabama at Birmingham | public educational institution of the United States, public research university | — | 1969 |
| University of Alabama in Huntsville | public educational institution of the United States, university | — | 1950 |
| University of Alaska System | state university system | Fairbanks | 1917 |
| University of Arkansas for Medical Sciences | medical university, public educational institution of the United States | — | 1879 |
| University of California, Berkeley | United Nations Depository Library, public educational institution of the United States, land-grant university, public research university | Berkeley | March 23, 1868 |
| University of California, Berkeley School of Law | law school | — | 1894 |
| University of California, Irvine | public educational institution of the United States, public research university | — | 1965 |
| University of California, Los Angeles | public educational institution of the United States, public research university | Los Angeles | May 23, 1919 |
| University of California, Merced | public educational institution of the United States, doctoral university: higher research activity, university, census-designated place in the United States | — | 2002 |
| University of California, San Diego | public educational institution of the United States, public university | — | November 18, 1960 |
| University of Central Arkansas | public educational institution of the United States, university | — | 1907 |
| University of Central Missouri | public educational institution of the United States, university | — | 1871 |
| University of Charleston | private not-for-profit educational institution, private university | — | 1888 |
| University of Chicago Law School | law school | Chicago | 1902 |
| University of Chicago Press | book publisher, university press | Chicago | 1891 |
| University of Cincinnati | public educational institution of the United States, public research university | — | 1819 |