| 3D Systems | Rock Hill | 1986 |
| 3M | Maplewood | 1902 |
| AbbVie | North Chicago | April 10, 2012 |
| ABC Family Worldwide | Burbank | 1990 |
| ABCorp | Stamford | 1795 |
| Abercrombie & Fitch | New Albany | 1892 |
| AbioMed | Danvers | 1981 |
| Ace Hardware | Oak Brook | 1924 |
| Acxiom | Wilmington, Conway | 2018 |
| Adaptec | Sunnyvale | 1981 |
| Adscape | San Francisco | 2006 |
| Advance Auto Parts | Roanoke | 1932 |
| Affliction Entertainment | Los Angeles | 2008 |
| Aflac | Columbus | 1955 |
| Airbnb | San Francisco | 2008 |
| Airstream | Jackson Center | 1931 |
| Airtable | San Francisco | 2012 |
| Akamai Technologies | Cambridge, Massachusetts | 1998 |
| Alamo Rent a Car | Clayton | 1974 |
| Albertsons | Boise | 1939 |
| Aldus | Seattle | February 1, 1984 |
| Alexion Pharmaceuticals | Cheshire | 1992 |
| AllianceBernstein | Nashville | 1967 |
| Allis-Chalmers | Milwaukee | 1901 |
| Allison Engine Company | Indianapolis | 1915 |
| Altair Engineering | Troy | 1985 |
| Amaze Entertainment | Kirkland | 1997 |
| Amazon | Seattle | July 5, 1994 |
| Amazon Lab126 | Cupertino | 2004 |
| Amazon Robotics | Massachusetts | January 1, 2003 |
| Amblin Television | Universal City | July 31, 1984 |
| American Automobile Association | Heathrow | 1902 |
| American Axle | Detroit | 1994 |
| American Bridge Company | Coraopolis | 1900 |
| American Cyanamid | Wayne | 1907 |
| American Electric Power | Columbus, Jersey City | August 1927 |
| American Express | New York City | 1850 |
| American International Group | New York City | 1919 |
| American Locomotive Company | Schenectady, New York City | June 24, 1901 |
| American Tourister | Rhode Island | 1933 |
| American Type Founders | Elizabeth | 1892 |
| American Wrestling Association | Minneapolis | 1960 |
| Amgen | Thousand Oaks | 1980 |
| Amkor Technology | Tempe | 1968 |
| Analog Devices | Norwood | 1965 |
| Anchor Brewing Company | San Francisco | 1896 |
| Aniplex of America | Santa Monica | 2005 |
| Anschutz Entertainment Group | Los Angeles | — |