| 20th Television Animation | Los Angeles | May 19, 1999 |
| 3Com | Marlborough | 1979 |
| 7-Eleven | Dallas, Irving | 1927 |
| A. T. Cross Company | Lincoln | 1846 |
| Abercrombie & Fitch | New Albany | 1892 |
| AbioMed | Danvers | 1981 |
| Access Systems Americas | Reston | — |
| Ace Hardware | Oak Brook | 1924 |
| AddThis | Vienna | 2006 |
| AdMob | Mountain View | 2006 |
| Adobe | San Jose | February 28, 1982 |
| Advance Auto Parts | Roanoke | 1932 |
| Advent International | Boston | 1984 |
| Aetna | Hartford | 1853 |
| Affirm Films | Culver City | 2008 |
| Ageia | Santa Clara | 2002 |
| Agilent Technologies | Santa Clara | 1999 |
| Airbnb | San Francisco | 2008 |
| Airtable | San Francisco | 2012 |
| Aksys Games | Torrance | July 14, 2006 |
| Alamo Rent a Car | Clayton | 1974 |
| Albemarle Corporation | Baton Rouge | 1994 |
| Albertsons | Boise | 1939 |
| Alcon Entertainment | Los Angeles | 1997 |
| Allen-Bradley | Milwaukee | 1903 |
| AllianceBernstein | Nashville | 1967 |
| Allis-Chalmers | Milwaukee | 1901 |
| Allison Engine Company | Indianapolis | 1915 |
| Allstate | Northbrook | April 17, 1931 |
| Ally Financial | Detroit, New York City | 1919 |
| Alpha Tomo Global Resoures Sdn Bhd | Milwaukee | 1948 |
| Amazon Robotics | Massachusetts | January 1, 2003 |
| Amazon Web Services | Seattle | March 2006 |
| Amblin Television | Universal City | July 31, 1984 |
| Amdahl Corporation | Sunnyvale | October 19, 1970 |
| American Cyanamid | Wayne | 1907 |
| American Eagle Outfitters | Pittsburgh | 1977 |
| American LaFrance | Summerville | 1873 |
| American Locomotive Company | Schenectady, New York City | June 24, 1901 |
| American Society for Testing and Materials | West Conshohocken | 1961 |
| American Type Founders | Elizabeth | 1892 |
| Amgen | Thousand Oaks | 1980 |
| Amkor Technology | Tempe | 1968 |
| Amlogic | Santa Clara | 1995 |
| Ampex | Redwood City | 1944 |
| AMR Corporation | Fort Worth | October 1, 1982 |
| Analog Devices | Norwood | 1965 |
| Ancestry.com Inc. | Lehi | 1983 |