| 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 |
| J. B. Hunt | business, public company | Lowell | 1961 |
| J. C. Penney | department store chain, organization, business, public company | Plano | 1902 |
| Jack Daniel's | distillery, business, enterprise | Jack Daniel's Distillery | 1866 |
| Jack in the Box | fast food restaurant chain, public company | San Diego | 1951 |
| Jackson Guitars | business, musical instrument manufacturing company | Scottsdale | 1980 |
| Jacksonville University | private not-for-profit educational institution, university | Palm Beach Gardens | 1934 |
| Jakks Pacific | business, public company | Malibu | 1995 |
| Jamba | restaurant chain, business, public company | Frisco | 1990 |
| James Madison University | public educational institution of the United States, public university | Harrisonburg | 1908 |
| Janet | airline | Las Vegas | 1972 |
| Jeppesen | business | Inverness | 1934 |
| Jerry Bruckheimer Films | film production company, independent business | Santa Monica | 1990 |
| Jet | brand, business, gas station chain | — | — |
| Jewish Theological Seminary of America | Jewish seminary, private not-for-profit educational institution | New York City | 1886 |
| Jewish Virtual Library | virtual library, online encyclopedia | — | 1998 |
| Jim Crockett Promotions | business | Charlotte | 1931 |
| John Carroll University | Jesuit university, private not-for-profit educational institution | — | 1886 |
| John F. Kennedy Presidential Library and Museum | museum, library | — | 1979 |
| John F. Kennedy School of Government | public policy school, graduate school, private school | Cambridge | 1936 |
| John Hancock Insurance | business | Boston | 1862 |
| Johnny Rockets | fast food restaurant chain, restaurant chain | Lake Forest | 1986 |