States Split Between Time Zones: Where the Lines Fall

A time zone map drawn with a ruler would be tidy and useless. In practice the boundaries wander, and the states split between time zones are the reason: about a dozen of them carry the line straight through their own territory, so two towns in the same state can keep clocks an hour apart. Anyone booking an appointment in western Kentucky or the Florida panhandle learns this quickly.

This article lists the states split between time zones, describes roughly where each boundary runs, and explains why the line follows county borders and trade routes rather than a meridian. To see how the affected zones compare at this moment, open the live US time board.

Which Are the States Split Between Time Zones?

Around thirteen states are divided. Florida, Michigan, Indiana, Kentucky and Tennessee straddle the Eastern and Central boundary. Kansas, Nebraska, North Dakota, South Dakota and Texas straddle Central and Mountain. Idaho, Oregon and Nevada straddle Mountain and Pacific, and Alaska has a second zone in the far Aleutians.

In almost every case the smaller portion is the exception. A handful of counties, sometimes only one, sits on the far side of the line because its people shop, bank, commute and watch television in a neighbouring state.

Michigan belongs on the list as well, since four Upper Peninsula counties along the Wisconsin border keep Central Time while the rest of the state keeps Eastern. Nobody planned any of this. The zones were laid over an existing map of counties and railway divisions, and every irregularity since has come from a local petition rather than a national redesign.

Where the Eastern and Central Line Falls

The eastern group of split states shares a pattern: the populous side keeps Eastern Time and a western or panhandle fringe keeps Central.

• Florida: The panhandle west of the Apalachicola River runs on Central Time, so Pensacola is an hour behind Tallahassee and Miami.
• Michigan: Four Upper Peninsula counties along the Wisconsin border keep Central Time, while the rest of the state, including Detroit, keeps Eastern.
• Indiana: Twelve counties are on Central Time, clustered near Chicago in the north-west and near Evansville in the south-west.
• Kentucky: The line runs down the middle, leaving Louisville and Lexington on Eastern and Bowling Green and Paducah on Central.
• Tennessee: East Tennessee, including Knoxville and Chattanooga, is Eastern; Nashville and Memphis are Central.

Kentucky and Tennessee are the two states split between time zones where the division is close to an even halving of the population, which is why both have long-running local debates about unifying.

Where the Central and Mountain Line Falls

On the plains the split is lopsided. Each of these states keeps its cities on Central Time and hands a thinly populated western edge to Mountain Time, following the point where the high plains begin.

Nebraska's panhandle around Scottsbluff is on Mountain Time, as are the four westernmost counties of Kansas, the south-western corner of North Dakota, and roughly the western half of South Dakota, including the Black Hills and Rapid City. Texas is the most extreme case: the entire state keeps Central Time apart from El Paso and most of neighbouring Hudspeth County, which look towards New Mexico and keep Mountain. Details of the larger zone are set out in the guide to Central Time.

The Western and Northern Splits

Idaho is cut across the middle. The northern panhandle above the Salmon River keeps Pacific Time along with Spokane and the interior north-west, while Boise and southern Idaho keep Mountain Time.

Oregon is almost entirely Pacific, with the exception of most of Malheur County in the far east, which keeps Mountain Time because it belongs to the economic orbit of Boise. Nevada is almost entirely Pacific too, save for the small town of West Wendover on the Utah line, which was moved to Mountain Time so it could share a clock with Salt Lake City. Alaska keeps a single Alaska Time zone across almost its whole territory, with only the western Aleutian Islands on Hawaii–Aleutian Time.

Why Do Time Zone Boundaries Follow County Lines?

Because the law tells the boundary to follow commerce, and counties are the smallest units in which commerce is measured. The Department of Transportation, which sets the boundaries, judges petitions largely on where the area's business, media and travel naturally point.

The habit is older than the department. When the railways imposed standard time in the nineteenth century, and again when the Standard Time Act of 1918 gave the zones legal force, lines were drawn along railway divisions and county borders because those matched how goods and people actually moved. The Uniform Time Act of 1966 transferred the authority to the Department of Transportation and kept the same test. A county whose residents commute into a neighbouring metropolitan area has a strong case to move; one that merely dislikes early sunsets does not.

Daylight saving is handled separately from the boundary question, and the same 1966 law allows a state that lies in two zones to exempt only the portion in one of them. That provision exists because of the difficulties Indiana created, and it has never been widely used: every one of the split states now observes the seasonal change across its whole territory. The only year-round exceptions in the country are Arizona, apart from the Navajo Nation, and Hawaii, so a split state is at least consistent with itself twice a year even when it is not consistent internally about the hour.

Living in the States Split Between Time Zones

For residents, the boundary is a daily fact rather than a curiosity. Broadcast schedules, court sittings, school start times and store opening hours all have to be stated with a zone attached.

A few practical rules help anyone dealing with a split state.

• Ask for the town, not the state, when confirming a time; "Kentucky time" means nothing.
• Assume the state's largest city may not represent the whole state's clock.
• Remember that a county can and occasionally does move, so old assumptions expire.
• Check whether the area also sits near a daylight saving exception, which compounds the confusion.

The most instructive case of all is examined in Indiana time zone history, and the wider structure of the zones is set out in US time zones explained. For the states on the western side of the divide, see Central Time zone states.

Conclusion

The states split between time zones are divided because the boundary was drawn to follow trade rather than geometry: Florida, Michigan, Indiana, Kentucky and Tennessee on the Eastern and Central line, Kansas, Nebraska, the Dakotas and Texas on the Central and Mountain line, and Idaho, Oregon, Nevada and Alaska further west. In every case the exception county looks towards a neighbouring city, and the Department of Transportation will move a line when that pull is strong enough. Compare the zones on the live US time board, or browse every clock at ustime.now.