There are over 1,600 studios and publishers in the U.S., says the ESA
The Entertainment Software Association has crunched the numbers and says that there are 1,641 game development studios and publishers which operate 1,871 offices across the U.S. California is in the lead with 546, followed by Texas (196), New York (154), Washington (149) and Massachusetts (92).
What the ESA doesn't say is precisely what defines inclusion on the list; it's likely that there are many more solo and hobbyist developers that were not included. It also declined to distinguish between publishers that do or do not maintain development facilities, instead lumping everything together into one total.
The industry association also says that 406 U.S. colleges and universities offer game development degrees across 46 states. The ESA has prepared an infographic about game education in the U.S. that adds some detail to these basic numbers.