The division of the united states into standard time zones was first done by which group?

The railroad companies did it. Before 1883, in the United States, each town in the United States had its own schedule, since there was no radio or television, the time was decided by the inhabitants of an area; but this affected the railways a lot, because they had to print tickets with the schedule, and it was not possible because each town or area had different schedules. Thus, in 1883, railroad companies worked together with the government to establish the Standard Time, which would divide the country into four time zones: Eastern Standard Time, mountain Time, central Time and standard pacific Time.