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Mexico’s territory, 1821 to today

How big Mexico was, and what it lost to the north

In 1821 Mexico reached the 42nd parallel, where Oregon begins today. By 1848 more than half of that land belonged to the USA.

4,430,000 km²1,710,000 sq mi · Mexico in 1821, without Central America
2,472,000 km²954,000 sq mi · lost to the USA by 1854, settled by the treaties of 1848 and 1853
55.8%of the Mexico of 1821, lost to the USA
1,958,000 km²756,000 sq mi · Mexico today, by the same outlines

Mexico in 1821, set against Mexico today

Interactive maptap or click a state to open its page

AguascalientesBaja CaliforniaBaja California SurCampecheChiapasChihuahuaCoahuilaColimaDurangoGuanajuatoGuerreroHidalgoJaliscoMexico CityMichoacánMorelosNayaritNuevo LeónOaxacaPueblaQuerétaroQuintana RooSan Luis PotosíSinaloaSonoraState of MexicoTabascoTamaulipasTlaxcalaVeracruzYucatánZacatecasCaliforniaArizonaNew MexicoColoradoWyomingOklahomaCeded 1848after the Mexican-American WarTexas 1836USA 1845Texas claimto the Rio GrandeLa MesillaGadsden Purchase, 1853-5442nd parallel, 1821where Oregon begins todayMexico todaytap a state
Texas, held 1836, USA 1845Texas claim to the Rio GrandeCeded 1848La Mesilla (Gadsden Purchase), 1853-54Mexico today (tap a state)The 1819 line Mexico inherited in 1821
The white line is the border Spain and the USA agreed in 1819 (in force 1821), which Mexico inherited at independence and confirmed by the Treaty of Limits of 1828: the Sabine, the Red River, the 100th meridian, the Arkansas and the 42nd parallel to the Pacific. Today’s USA state lines are drawn faintly for reference; they did not exist then. Tap a Mexican state to open its history. 21

Five moments, one country

Gold is Mexico at that date, as on the big map. Colour is land already gone; hatching is land claimed by others but still held by Mexico. Swipe for all five, 1822 to today.

1822

The largest Mexico

Central America joins the Mexican Empire on 5 January 1822: Mexico reaches from the 42nd parallel to Costa Rica. 62

1823-1836

Central America leaves

Central America declares itself independent on 1 July 1823; Chiapas stays with Mexico, confirmed in 1824. Soconusco stays disputed until 1842. 67

1836

Texas breaks away

Texas holds the land east of the Nueces and claims everything to the Rio Grande and up to the 42nd parallel (hatched). The USA annexes it in 1845. 510

1848

The war's price

After the Mexican-American War, the Treaty of Guadalupe Hidalgo (2 February 1848) sets the line on the Rio Grande, the Gila and a straight line to the Pacific south of San Diego: California, Nevada, Utah and most of Arizona and New Mexico go north. 38

1854-today

La Mesilla, then today

La Mesilla is sold for US$10 million (signed 30 December 1853, in force 30 June 1854). Since then the line has moved only by river-bank exchanges, settled in 1970, and the Chamizal, returned in 1967. 4914

What was lost and gained, date by date

Share is of the Mexico of 1821 without Central America. A minus sign is land lost. The 1848 row counts the whole Texas claim, including the land Texas held from 1836.

DateWhat changedAreaShare of 1821Sources
27 Sep 1821Independence: Mexico inherits New Spain’s north, bounded by the 1819 line.4,430,000 km²100%21
5 Jan 1822Central America joins the Mexican Empire.+421,000 km²+9.5%6
1 Jul 1823Central America declares itself independent; Chiapas stays with Mexico (confirmed 1824).−421,000 km²−9.5%6
1836Texas breaks away and holds the land east of the Nueces; Mexico does not recognise it.−355,000 km²−8.0%5
1842Soconusco joins Mexico (Guatemala accepts the line in 1882).a gain, not measured here7
29 Dec 1845The USA annexes Texas (resolution of 1 March, statehood 29 December) and takes up its claim to the Rio Grande and the 42nd parallel, with the boundary left open. Mexico rejects it.claimed105
May 1846The Mexican-American War: the USA declares war on 13 May 1846; its army takes Mexico City in September 1847.58
2 Feb 1848Treaty of Guadalupe Hidalgo: Mexico accepts the Texas line on the Rio Grande (the whole Texas claim, 993,000 km², 22.4%) and cedes California and New Mexico.−2,375,000 km²−53.6%38
30 Dec 1853La Mesilla (the Gadsden Purchase), in force 30 June 1854, for US$10 million.−94,000 km²−2.1%49
28 Jan 1931Clipperton Island, claimed by Mexico since 1897 (not part of the Mexico of 1821), is awarded to France by arbitration.under 10 km²15
28 Oct 1967The Chamizal, at El Paso and Ciudad Juárez, is handed back to Mexico (630 acres handed over, 193 of Cordova Island returned).+ about 1.8 km² net14
TodayMexico, by the same outlines.1,958,000 km²44.2%1

What these maps do not show

A claim is not control

Much of the north painted as Mexican in 1821 was Comanche and Apache country. Comanchería ran from today’s New Mexico and West Texas into Oklahoma, Kansas and Colorado, and in the 1830s and 1840s Comanche raids reached deep into Mexico. Apachería stretched from north of the Arkansas into what is now northern Mexico. The line on the map is what governments signed; on the ground, these nations held much of it. 1213

Yucatán left twice

Yucatán declared itself independent in 1841, kept its own government under an 1843 agreement, and separated again on 1 January 1846, at one point offering itself to the USA, Britain and Spain. With the Caste War, which began in July 1847, it asked Mexico for help and rejoined the federation on 17 August 1848. The maps keep it inside Mexico throughout. 11

Lines that were drawn simply

Mexican Texas had no fixed northern edge. We show the land Texas held as east of the Nueces and, above the river’s source, east of that meridian. Soconusco, disputed from 1824 to 1842, is marked with a ring, not drawn. Small changes do not show at this scale: the Chamizal, Clipperton and the Mexico-Guatemala and Belize lines settled in 1882 and 1893. 71415

La Mesilla had two lines

The 1848 treaty described the New Mexico line from a map with errors. In 1851 the two boundary commissioners agreed a line at 32° 22′, which Mexico stood by and Washington rejected; the USA read the treaty at 31° 52′. The strip between them (lightly hatched) was settled by the 1853 sale. Counted from the USA’s reading, the sale is 79,000 km²; counted from the line Mexico held, 94,000 km². 349

How these maps were drawn

These are our own maps. The outlines are Natural Earth’s public-domain 1:10m countries, states and rivers. The historical lines follow the treaty texts: the 1819 line along the Sabine, the Red River, the 100th meridian, the Arkansas and the 42nd parallel; the 1848 line along the Rio Grande and the Gila; the 1853 line as Mexico and the USA hold it today. Areas are measured on an equal-area projection and checked against the published figures below. 1234

MeasureOursPublishedGap
Ceded in 1848, without Texas1,382,000 km²1,360,000 km²+1.6%
La Mesilla, from the USA's reading of the 1848 line79,000 km²77,000 km²+2.4%
La Mesilla, from the line Mexico held (the gap is the disputed strip)94,000 km²77,000 km²+21.9%

Share lost, counting Texas: ours 55.8%; published, about 55%. 589

Mexico by state: the history of each of the 31 states and Mexico City →

Sources

  1. Natural Earth, 1:10m countries, states and rivers (public domain): the outlines and the rivers the treaty lines follow. Read 4 Nov 2026.
  2. Adams-Onís Treaty, 22 Feb 1819, Article III (the line from the Sabine to the 42nd parallel), Avalon Project, Yale. Read 4 Nov 2026.
  3. Treaty of Guadalupe Hidalgo, 2 Feb 1848, Article V; ratifications exchanged 30 May 1848, Avalon Project, Yale. Read 4 Nov 2026.
  4. Gadsden Purchase (Treaty of La Mesilla), 30 Dec 1853, Article I; proclaimed 30 Jun 1854, Avalon Project, Yale. Read 4 Nov 2026.
  5. Wikipedia, Territorial evolution of Mexico (dates, about 55% ceded counting Texas, what the maps cannot show). Read 4 Nov 2026.
  6. Wikipedia, Mexican annexation of Central America (5 Jan 1822; 1 Jul 1823; Chiapas confirmed in 1824). Read 4 Nov 2026.
  7. Wikipedia, Soconusco (disputed after 1824; joined Mexico in 1842; border treaty with Guatemala, 1882). Read 4 Nov 2026.
  8. Wikipedia, Mexican Cession (about 525,000 sq mi, 1.36 million km², without Texas). Read 4 Nov 2026.
  9. Wikipedia, Gadsden Purchase (29,640 sq mi, 76,800 km²; US$10 million). Read 4 Nov 2026.
  10. Wikipedia, Texas annexation (joint resolution 1 Mar 1845; statehood 29 Dec 1845). Read 4 Nov 2026.
  11. Wikipedia, Republic of Yucatán (independence 1841; separation again 1 Jan 1846; rejoined 17 Aug 1848). Read 4 Nov 2026.
  12. Wikipedia, Comancheria (about 1770 to 1850; raids deep into Mexico in the 1830s and 1840s). Read 4 Nov 2026.
  13. Wikipedia, Apacheria (from north of the Arkansas into today's northern Mexico). Read 4 Nov 2026.
  14. Wikipedia, Chamizal dispute (convention 29 Aug 1963; 630 acres handed to Mexico on 28 Oct 1967, 193 acres of Cordova Island returned). Read 4 Nov 2026.
  15. Wikipedia, Clipperton Island (arbitration award for France, 1931). Read 4 Nov 2026.