Time Zones in the United States

In the early history of the United States, telling time was not always easy. Communities set their own clocks, using the Sun as their guide. This resulted in hundreds of regional times, and in some larger cities, clocks could vary between neighborhoods. Things got more complicated—and dangerous—with the advent of trains. Railroad lines often used different timetables, raising the possibility of collisions. To improve safety and efficiency, railroad companies adopted a standardized system of four time zones—Eastern, Central, Mountain, and Pacific—on November 18, 1883. The new system was soon adopted by numerous cities, and in 1918 the U.S. government officially recognized these time zones—and created one for Alaska—with the passage of the Standard Time Act. This legislation also established federal Daylight Saving Time. The Hawaii-Aleutian time zone was later added, as were those for the country’s territories: Atlantic, Samoa, and Chamorro.

Below is a list of states and territories in the various time zones. Asterisks indicate states that are in more than one time zone.