The Boundary That Splits 20 States, Two Countries, and One Clock
Chicago and Mexico City share a clock in January. In July they are an hour apart. The line that decides this runs from the Manitoba tundra to the Gulf of Mexico, cutting through living rooms, school districts and stock exchanges.
Central Time is not a neat rectangle. It jogs at county lines, follows a river for a stretch, then veers west to accommodate a rail corridor. The zone holds 12,294,193 people in Mexico City, 2,664,452 in Chicago, and 2,314,157 in Houston. About 85 million Americans live inside it, plus millions more in Canada, Mexico and Central America.
Which states split between Central and Eastern Time?
The boundary with Eastern Time is a jagged thing. It slices Indiana, Kentucky, Tennessee, Michigan and Florida into two clocks.
Florida: The Apalachicola River divides the Panhandle from the peninsula. Pensacola and Panama City run on Central Time. Tallahassee and Jacksonville do not.
Indiana: Twelve counties in the northwest corner (the Gary and Hammond industrial strip, pulled toward the city on Lake Michigan) and the southwest corner (the Evansville area) observe Central Time. The rest of the state has been Eastern since a DOT ruling that took full effect in 2007.
Kentucky: Louisville and Bowling Green sit on the Central side. Lexington, Frankfort and the eastern coalfields run an hour ahead. The seam follows the boundary between the Mississippian Plateau and the Appalachian foothills.
Michigan: Four counties in the Upper Peninsula bordering Wisconsin use Central Time. Menominee, Dickinson, Iron and Gogebic. The rest of the state, including Detroit, is Eastern.
Tennessee: Memphis and Nashville are Central. Knoxville and the Tri-Cities are Eastern. The switch happens along the Cumberland Plateau, roughly at the line where the Tennessee River bends south.
Which states split between Central and Mountain Time?
The western boundary is just as irregular. It runs from the Canadian border through the Great Plains to the Rio Grande.
Nebraska: The eastern two-thirds (Omaha, Lincoln, Grand Island) use Central Time. The Panhandle (Scottsbluff, Chadron) switches to Mountain. The dividing line runs roughly along the 100th meridian.
Kansas: Sherman, Wallace, Greeley and Hamilton counties, the four that touch Colorado, observe Mountain Time. The remaining counties are Central.
Texas: Most of the state is Central. El Paso County and Hudspeth County in the far west use Mountain Time, aligning with Ciudad Juárez across the border.
North Dakota and South Dakota: The southwestern counties of both states (including Rapid City) run on Mountain Time. The eastern majority, including Sioux Falls and Fargo, stays Central.
Cities that anchor the zone
Central Time holds some of the continent's largest population centres. The biggest, by city-proper population:
| City | Population | IANA zone |
|---|---|---|
| Mexico City | 12,294,193 | America/Mexico_City |
| Chicago | 2,664,452 | America/Chicago |
| Houston | 2,314,157 | America/Chicago |
| Iztapalapa | 1,835,486 | America/Mexico_City |
| Puebla | 1,692,181 | America/Mexico_City |
| Ecatepec de Morelos | 1,645,352 | America/Mexico_City |
| Santiago de Querétaro | 1,594,212 | America/Mexico_City |
| León de los Aldama | 1,579,803 | America/Mexico_City |
| San Antonio | 1,526,656 | America/Chicago |
| Zapopan | 1,476,491 | America/Mexico_City |
Mexico City alone accounts for over 12 million people. The combined weight of the top four US metros (Chicago, Dallas, Houston, San Antonio) exceeds 7.8 million city-proper residents.
Chicago: the reference point for US Central Time
Chicago's IANA zone is America/Chicago. The city proper holds 2,664,452 people; the metro area is larger still. The Chicago Mercantile Exchange and Chicago Board of Trade run on this clock. US futures markets open at 8:30 a.m. Central, a half-hour before the New York Stock Exchange opens in Eastern Time.
When a broadcaster says "8/7c," the "c" is Chicago. The city sits at the southwest corner of Lake Michigan, a transport hub where six Class I railroads converge. For scheduling calls across US time zones, Chicago is the default reference.
Why Dallas, Houston and San Antonio share a clock but not a coastline
Texas is the largest state that sits almost entirely in Central Time. The three anchors of the Texas Triangle:
- Dallas: 1,326,087 in the city proper, IANA America/Chicago.
- Houston: 2,314,157, IANA America/Chicago.
- San Antonio: 1,526,656, IANA America/Chicago.
Only El Paso and Hudspeth counties in the far west use Mountain Time. The rest of Texas, from the Louisiana border to the Panhandle, runs on the same hour hand. That covers energy, aerospace, healthcare and the busiest inland port in the US (Houston).
What other major US cities are in the Central Time Zone?
Beyond the Texas Triangle, Central Time includes a string of metros that anchor the Mississippi and Missouri river corridors:
- Minneapolis and St. Paul: America/Chicago.
- St. Louis: America/Chicago.
- Kansas City: America/Chicago.
- New Orleans: America/Chicago.
- Oklahoma City: America/Chicago.
- Memphis: America/Chicago.
These cities are freight hubs, medical centres and music capitals. They sit on the same clock as Chicago and Houston.
Mexico City: the largest city in the zone, and the one that stays put
Mexico City (Ciudad de México) holds 12,294,193 people. Its IANA zone is America/Mexico_City. The city sits at 2,240 metres above sea level, at coordinates 19.428, -99.128.
On the March equinox (20 March 2026): sunrise 06:41, sunset 18:47, 12 hours 6 minutes of daylight. On the June solstice (21 June 2026): sunrise 05:58, sunset 19:16, 13 hours 18 minutes of daylight. On the September equinox (22 September 2026): sunrise 06:24, sunset 18:33, 12 hours 9 minutes of daylight. On the December solstice (21 December 2026): sunrise 07:05, sunset 18:03, 10 hours 57 minutes of daylight.
Mexico abolished daylight saving time nationally in October 2022. Mexico City is now on permanent CST (UTC−6). It does not spring forward.
The border zone where Mexico still follows the US clock
Northern border municipalities within roughly 20 kilometres of the US line continue to observe US DST. The IANA zones that track this:
- Matamoros (across from Brownsville, Texas): America/Matamoros
- Monterrey (1,135,512 people): America/Monterrey
- Ojinaga (across from Presidio, Texas): America/Ojinaga
This creates a seasonal split inside Mexico:
- November to March: Mexico City and Chicago both run CST (UTC−6). Same time.
- March to November: Chicago springs forward to CDT (UTC−5). Mexico City stays on CST (UTC−6). One hour apart.
When it is 10:00 a.m. in Chicago in July, it is 09:00 in Mexico City.
Canada's Central Time: Saskatchewan's permanent summer
Manitoba (America/Winnipeg) follows the US DST schedule. Parts of Nunavut (America/Rankin_Inlet, America/Resolute) and northwestern Ontario also use Central Time.
Saskatchewan is the outlier. The province sits geographically inside the Mountain Time zone but legally observes Central Standard Time year-round. No DST.
- Winter: Regina matches Chicago (CST, UTC−6).
- Summer: Regina stays on CST (UTC−6). Chicago moves to CDT (UTC−5). Regina is one hour behind.
The IANA zones are America/Regina and America/Swift_Current. Effectively, Saskatchewan is on permanent summer time relative to its longitude.
Central America: six countries, one offset, no clock changes
Six nations run on Central Standard Time all year. None observe DST:
| Country | IANA zone |
|---|---|
| Belize | America/Belize |
| Costa Rica | America/Costa_Rica |
| El Salvador | America/El_Salvador |
| Guatemala | America/Guatemala |
| Honduras | America/Tegucigalpa |
| Nicaragua | America/Managua |
They stay on UTC−6. They match Chicago in winter and lag one hour behind in summer.
Which states and provinces fall inside the zone?
Entirely in Central Time (US)
Alabama, Arkansas, Illinois, Iowa, Louisiana, Minnesota, Mississippi, Missouri, Oklahoma, Wisconsin.
Split between Central and Eastern
Florida (Panhandle), Indiana (12 counties), Kentucky (western half), Michigan (4 Upper Peninsula counties), Tennessee (western and middle).
Split between Central and Mountain
Kansas (4 western counties), Nebraska (western Panhandle), North Dakota (southwestern), South Dakota (western), Texas (El Paso and Hudspeth counties).
Canadian provinces and territories
Manitoba, Saskatchewan (CST year-round), parts of Nunavut, northwestern Ontario.
What time is it right now, and when do the clocks shift?
On 1 October 2026 the zone is on Central Daylight Time (CDT), UTC−5.
Spring forward: Sunday 8 March 2026 at 02:00 local. Clocks go forward 60 minutes to 03:00. CST becomes CDT. Fall back: Sunday 1 November 2026 at 02:00 local. Clocks go back 60 minutes to 01:00. CDT becomes CST.
2027 dates: Spring forward Sunday 14 March 2027 at 02:00 local. Fall back Sunday 7 November 2027 at 02:00 local.
The IANA zones using the America_Central metazone:
America/Bahia_Banderas, America/Belize, America/Chicago, America/Chihuahua, America/Costa_Rica, America/El_Salvador, America/Guatemala, America/Indiana/Knox, America/Indiana/Tell_City, America/Managua, America/Matamoros, America/Menominee, America/Merida, America/Mexico_City, America/Monterrey, America/North_Dakota/Beulah, America/North_Dakota/Center, America/North_Dakota/New_Salem, America/Ojinaga, America/Rankin_Inlet, America/Regina, America/Resolute, America/Swift_Current, America/Tegucigalpa, America/Winnipeg.
How the zone lines up with the rest of the world
On 15 January 2026, relative to CST (UTC−6):
New York +1 hour. Los Angeles −2 hours. London +6 hours. Paris +7 hours. Dubai +10 hours. Mumbai +11.5 hours. Singapore +14 hours. Tokyo +15 hours. Sydney +17 hours. Johannesburg +8 hours. São Paulo +3 hours.
On 15 July 2026, relative to CDT (UTC−5):
New York +1 hour. Los Angeles −2 hours. London +6 hours. Paris +7 hours. Dubai +9 hours. Mumbai +10.5 hours. Singapore +13 hours. Tokyo +14 hours. Sydney +15 hours. Johannesburg +7 hours. São Paulo +2 hours.
London stays 6 hours ahead in both seasons because British Summer Time shifts with CDT. Dubai and Mumbai, which do not observe DST, close the gap by one hour in summer. Sydney's gap shrinks from 17 to 15 hours because the southern hemisphere summer is the northern winter.
What "CST" actually means, and why it causes fights
CST stands for Central Standard Time (UTC−6). CDT stands for Central Daylight Time (UTC−5). "Central Time" (CT) is the umbrella term that covers both.
Three common mix-ups:
- Saying "CST" in July. A meeting invite that reads "2:00 p.m. CST" in August is technically wrong. The correct abbreviation is CDT. Most people still understand it.
- CST vs China Standard Time. CST also means China Standard Time (UTC+8). In international scheduling, specify "America/Chicago" or "UTC−6" to avoid a 14-hour error.
- Assuming all of Mexico springs forward. Since 2023, most of Mexico does not. Mexico City is on permanent CST. Only the northern border strip follows the US DST calendar.
The Sunshine Protection Act and the push to lock the clock
The US Senate passed the Sunshine Protection Act in 2022. It would make daylight saving time permanent. The bill stalled in the House and was reintroduced. As of early 2026, it has not become law.
If enacted, Central Time would stay on UTC−5 year-round. No more falling back. The trade-off: darker winter mornings, especially on the zone's western edge. Some states have passed trigger laws that would adopt permanent DST if Congress authorises it. Permanent standard time (UTC−6 year-round) remains legal for any state to adopt without federal action.
What time do things actually happen?
Business hours: Offices typically run 8:00 a.m. to 5:00 p.m. CT. The "golden hour" for calls across all four mainland US zones is 12:00-1:00 p.m. CT.
Markets: Chicago Mercantile Exchange and Chicago Board of Trade operate on CT. The New York Stock Exchange (9:30 a.m., 4:00 p.m. ET) translates to 8:30 a.m., 3:00 p.m. CT.
Schools: Elementary and high schools typically start between 8:00 a.m. and 8:30 a.m. In the weeks after the spring forward, children in much of the zone walk to school or wait for buses in darkness.
Broadcast: "8/7c" means 8:00 p.m. Eastern, 7:00 p.m. Central. Live events anchored to Eastern prime time (Super Bowl, Oscars, election night) start at 7:00 p.m. in the Central zone.
Meals: Lunch peaks at noon. Dinner runs 6:00-8:00 p.m., earlier in rural areas and the Midwest, later in larger cities.
Friday night football: High school games typically kick off at 7:00-7:30 p.m. CT.
The zone's economic weight
Central Time accounts for roughly 28% of US GDP. The anchors:
- Chicago: finance, futures, freight.
- Houston: energy, the Port of Houston, the Texas Medical Center.
- Dallas-Fort Worth: airlines, defence, logistics.
- Mexico City: government, manufacturing, media for a nation of over 120 million.
- The Great Plains: grain, livestock and ethanol, all priced and shipped on Central Time.
The zone is not a monolith. It spans Arctic tundra, tallgrass prairie, subtropical Gulf Coast and highland Mexico. But the clock ties them together, most of the year.