The History of Time Zones in the United States

Before the 1880s, US towns kept their own local solar time, set by the sun's position overhead. A traveler crossing the country by train could pass through dozens of slightly different local times in a single day, and railroads had to run their own separate time systems just to keep schedules coherent.

On November 18, 1883 — sometimes called 'the day of two noons' — American and Canadian railroads adopted a standardized system of four time zones across the continent, each exactly one hour apart. Towns gradually fell in line with the nearest railroad zone over the following years, even though it had no formal legal backing yet.

Congress made the zone system federal law with the Standard Time Act of 1918, which also introduced the country's first daylight saving time, adopted temporarily during World War I. Daylight saving was repealed after the war, reinstated during World War II as 'War Time,' and eventually standardized nationwide by the Uniform Time Act of 1966.

The current start/end dates — second Sunday in March, first Sunday in November — were set by the Energy Policy Act of 2005 and took effect in 2007, extending daylight saving by about a month compared to the previous rules.

Between the world wars and again after 1945, daylight saving became a local option, and different states, counties, and even individual cities set their own rules. Indiana became the best-known example of the resulting confusion, with some counties observing DST and others refusing it for decades even after the practice was otherwise standardized nationally.

The Uniform Time Act of 1966 finally imposed a single national schedule while still permitting states to opt out entirely — a compromise that produced the modern exceptions of Arizona and Hawaii, both of which chose to stay on standard time year-round.

That same law also established the Department of Transportation as the federal body responsible for adjusting time zone boundaries, a role it still holds today whenever a county or region petitions to move from one zone to a neighboring one.