| IBM | software company, multinational corporation, technology company, professional services firm, organization, business, enterprise, public company | Armonk | June 16, 1911 |
| IBM Research | business, laboratory | — | 1945 |
| Icahn School of Medicine at Mount Sinai | private not-for-profit educational institution, medical school | — | 1963 |
| Icon Comics | publishing house, company | New York City | 2004 |
| Idaho State University | public educational institution of the United States, public research university | — | 1901 |
| IDW Publishing | comics publishing company | San Diego | 1999 |
| IEEE Computer Society | publishing house, organization | Washington, D.C. | 1963 |
| IGN | online newspaper, online film database, business, video game news website | San Francisco | September 29, 1996 |
| IIT Institute of Design | graduate school, design school, higher education institution, academic institution | — | 1937 |
| Illinois Central Railroad | transport company | Chicago | 1851 |
| Illinois Tool Works | business, public company | Glenview | 1912 |
| Illumina | business, enterprise, company, public company | San Diego | 1998 |
| Illumination | film production company | United States, Santa Monica, Los Angeles, California | January 17, 2007 |
| Imagic | video game publisher, video game developer | Los Gatos | 1981 |
| Imagine Entertainment | television production company, film production company | Beverly Hills | November 1985 |
| IMG | business | New York City | 1960 |
| Immediate Music | record label, business | Santa Monica | 1993 |
| Impressions Games | video game developer | Cambridge | 1989 |
| Incyte | business, enterprise, public company | Wilmington | 2001 |
| Indeed | review site, search engine, business, employment website | Austin | November 2004 |
| Independent Moving Pictures | film studio, organization | New York City | 1909 |
| Indiana State University | public educational institution of the United States, public university | Terre Haute | 1865 |
| Industrial Light & Magic | television production company, film studio, business | San Francisco, Letterman Digital Arts Center | May 1975 |
| IndyMac | savings and loan association, business, credit institution | Pasadena | July 16, 1985 |
| Infinity Ward | video game developer | Woodland Hills | 2002 |
| Inflection AI | business, company | Palo Alto | 2022 |
| Infocom | video game publisher, video game developer, business | Cambridge | June 22, 1979 |
| Infor Global Solutions | software company, business | New York City | 2002 |
| InnoCentive | business, enterprise | Waltham | 2001 |
| Inovio Pharmaceuticals | business, public company | Plymouth Meeting | 1983 |
| Insomniac Games | video game publisher, video game developer | Burbank | February 28, 1994 |
| Institute for Scientific Information | business, enterprise | Philadelphia | 1960 |
| Institute of Electrical and Electronics Engineers | engineering society, standards organization, trade association, nonprofit organization, publishing house, open-access publisher, charitable organization, professional association, learned society, academic publisher | Manhattan | January 1963 |
| Institute of Mathematical Statistics | mathematical society, publishing house, open-access publisher | — | 1935 |
| Integrated Device Technology | business, public company | San Jose | 1980 |
| Intel | business, public company | Santa Clara | July 18, 1968 |
| Inter-American Development Bank | multilateral development bank | Washington, D.C. | 1959 |
| Interactive Brokers | brokerage firm, public company | Greenwich | 1994 |
| Intercontinental Exchange | stock market, business, public company | Atlanta | May 11, 2000 |
| International | commercial vehicle manufacturer, enterprise, public company | Lisle | 1986 |
| International Center of Photography | nonprofit organization, art museum, art academy | New York City | 1974 |
| International Flavors & Fragrances | organization, business, public company | New York City | 1958 |
| International Society for Computational Biology | community, open-access publisher, scientific society, learned society | Leesburg | 1997 |
| International Typeface Corporation | type foundry, defunct organization | New York City | 1970 |
| Interpublic Group of Companies | business, enterprise, public company | New York City | 1961 |
| Intuit | software company, business, enterprise, public company | Mountain View | 1983 |
| Invicta Watch Group | business | Hollywood | 1837 |
| IRobot | business, enterprise, public company | Bedford | 1990 |
| Iron Lore Entertainment | video game developer | Boston | October 2000 |
| IShares | Product group, brand, business, public company | San Francisco | 2000 |
| Island Air (Hawaii) | airline | Honolulu | 1980 |
| It's a Laugh Productions | production company | Studio City | November 3, 2003 |
| ITT Corporation | business, enterprise, public company | Stamford | 1920 |