| Thermos L.L.C. | manufacturing company | Chicago, Minato | 1980 |
| ThinkFilm | film industry, film production company, film distributor | New York City | September 2001 |
| Thiokol | business, defunct organization | Trenton, Brigham City | 1929 |
| Thomas Built Buses | automobile manufacturer | High Point | 1972 |
| Thomas Edison State University | public educational institution of the United States, school, academic institution | — | 1972 |
| THQ | video game publisher, video game developer, public company | Agoura Hills, California | 1990 |
| THX | technical standard, business | San Rafael | 1983 |
| TIAA | insurance company, business | New York City | 1918 |
| Tibco Software | business, enterprise, public company | Palo Alto | 1997 |
| Tiffany & Co. | jewelry shop chain, business, public company | New York City | 1837 |
| Tiger Electronics | business, subsidiary company | Vernon Hills | 1978 |
| Tilted Mill Entertainment | video game developer | Framingham | 2001 |
| Time Inc. | business, enterprise | New York City | November 28, 1922 |
| Time Warner Cable | internet service provider, production company, business, enterprise, public company | New York City | 1989 |
| Timex Group USA | business | Middlebury, United States | 1854 |
| Titleist | business | Fairhaven | 1932 |
| TKO Group Holdings | business, company | New York City | September 12, 2023 |
| Tommy Hilfiger B.V. | privately held company, business, subsidiary company, enterprise, brick and mortar | New York City, Amsterdam | 1985 |
| Tor Books | book publisher, publishing house, imprint | Equitable Building | 1980 |
| Toro | business, enterprise, public company | Bloomington | 1914 |
| Total Nonstop Action Wrestling | business, enterprise, professional wrestling promotion | Nashville | January 4, 2024 |
| Touchstone Television | business | California | December 4, 2014 |
| Tower Records | business, chain | Sacramento | 1960 |
| Toys for Bob | video game developer | Novato | 1989 |
| Trader Joe's | supermarket chain, business, gourmet supermarket chain | Monrovia | 1958 |
| Trans Executive Airlines | airline | Honolulu | 1982 |
| Trans States Airlines | airline | United States, Bridgeton | 1985 |
| Trans World Airlines | airline | Fort Worth | 1926 |
| Transylvania University | private not-for-profit educational institution, private university | Lexington | 1780 |
| TriBeCa Productions | television production company, film production company | New York City | 1989 |
| Tribune Publishing | publishing house | Chicago | 2014 |
| Trimark Pictures | film production company, business | Santa Monica | 1985 |
| Trimble | business, enterprise, public company | Westminster | 1978 |
| Trinity Evangelical Divinity School | university | — | 1950 |
| Tripadvisor | travel website, website, business, enterprise, public company | Needham | February 14, 2000 |
| Tropicana Las Vegas | skyscraper, casino, hotel, music venue | — | 1957 |
| Trump International Hotel and Tower | skyscraper, hotel | — | 2009 |
| Trump Mobile | mobile virtual network operator, brand | — | June 16, 2025 |
| Trump Shuttle | airline | New York City | 1989 |
| Trump Steaks | business | New York City | May 8, 2007 |
| Trump University | business | New York City | 2005 |
| Tseng Labs | business, defunct organization | Pennsylvania | 1983 |
| Tulane University | private not-for-profit educational institution, university | New Orleans | 1834 |
| Turner Broadcasting System | production company, media company, business, enterprise | CNN Center | 1970 |
| Turnitin | website, business, anti-plagiarism software | Oakland | 1997 |
| Twilio | website, business, company, public company | San Francisco | 2008 |
| Two Steps from Hell | musical group, music organization, business, enterprise | Los Angeles | 2006 |
| U.S. Cellular | business, enterprise, public company | Chicago | 1983 |