This is a list of the evolution of the borders of the United States. This lists each change to the internal and external borders of the country, as well as status and name changes. It also shows the surrounding areas that eventually became part of the United States. Each stage has a map, to show what the specific makeup of the country was at any given time.
After achieving independence with the Treaty of Paris, the United States expanded westward, enlarging its borders seven times, with two major border adjustments, one each with colonies of the United Kingdom and Spain, and several small disputes. The original thirteen states grew into fifty states, most of which began as incorporated territories. The general pattern seen in this is of territorial expansion, carving of organized territories from the newly acquired land, modification of the borders of these territories, and eventual statehood. Only two states, Nevada and Missouri, grew appreciably after statehood, and five, Georgia, Massachusetts, North Carolina, Texas, and Virginia, lost land, in each case to form new states.
- This article does not include unincorporated territories and countries under free association. The fundamental difference between unincorporated and incorporated territories is that incorporated territories are considered to forever be under the jurisdiction of the United States Constitution, whereas it is possible for unincorporated territories to become independent. These are:
- Nations under Compacts of Free Association: Marshall Islands, Federated States of Micronesia, Palau.
- Unincorporated, organized territories: Guam, United States Virgin Islands.
- Commonwealths, another form of unincorporated and organized territory: Northern Mariana Islands, Puerto Rico (This is different from the term commonwealth used by some states.)
- American Samoa is unorganized, but has a constitution and self-government, making it functionally very similar to an organized territory.
- The United States Minor Outlying Islands, which are uninhabited, unorganized, and except for Palmyra Atoll, unincorporated.
- The former unincorporated territories of the Line Islands, Panama Canal Zone, the Commonwealth of the Philippines, and the Phoenix Islands.
- The Trust Territory of the Pacific Islands, a United Nations trusteeship granted to the United States following World War II. It has since dissolved, becoming the Marshall Islands, Federated States of Micronesia, the Northern Mariana Islands, and Palau.
- Various other unincorporated territories whose claims under the Guano Island Act have been abrogated by the United States Government.
- "Unorganized territory" is not a name; it simply means Congress has not passed an organic act for the territory. In most situations, the purpose of unorganized territory was to act as land for Native American settlement. Later, the last unorganized territory in the country was indeed referred to as "Indian Territory", though this is not an official name. The last territories acquired by the United States, Alaska, Hawaii, and the Mexican Cession, began unorganized, but not as land set aside for Native Americans, but simply because they had not been organized yet. Palmyra Atoll is the only remaining unorganized incorporated U.S. territory.
- Dotted lines on the borders mean that region is part of a country not fully shown on the map, since it's confined to the present-day borders of the United States. An exception is Oregon Country, which was shared land which extended beyond the area of the map.
- Some territorial disputes and borders from early in the United States' history are unclear. For example, the border between West Florida and East Florida seems unclear. For the purposes of simplicity, this article uses the original border, the Apalachicola River, even though later maps tended to move it west to the Perdido River. This is partly because the Organic Act for Florida specified that it included parts of both West and East Florida; if the border were the Perdido River, then Florida Territory would not have included any of West Florida, it having already been divided among Louisiana, Mississippi, and Alabama.
- Several very small changes are included in the list but not included in the maps.
- The switch of two extra counties from Virginia to West Virginia at the end of the American Civil War.
- The Alaska Boundary Dispute, since it arose from a total lack of surveying, rather than a dispute over the surveyed lines; it would also appear quite small on the map.
- When the Dakota Territory was created, it also included land south of 43° N and north of the Keya Paha and Niobrara rivers. This was transferred to the state of Nebraska on March 28, 1882.
- The two small adjustments to Indiana Territory.
- Various disputes along the Rio Grande with Mexico.
- Ratification of the Constitution, Confederacy formation and reconstruction are simplified to make the map simpler.
- March 4, 1789
The United States Constitution came into effect, forming the new nation. Note that the states ratified at different times, but to simplify the map, the final result is shown here.
The United States achieved independence from the Kingdom of Great Britain with the Treaty of Paris on September 3, 1783, which established that the thirteen colonies were sovereign and independent states. The borders were established by Article 2 of the treaty, but with a couple of issues. First, it stated that the border would run west from the Lake of the Woods to the Mississippi River - at the time, it was not known that the headwaters of the Mississippi lay south of such a line, so the border has since been taken to run south from the lake to the river.
Some peculiarities to point out to those familiar only with the current borders: Many states had sea-to-sea grants from the British crown that they would not give up easily, so prior to this date, they ceded this land to the federal government in exchange for their Revolutionary War debts. However, Georgia did not do so until much later, and Connecticut ceded most land but kept its Western Reserve. Virginia ceded its claim to the territory north and west of the Ohio River, and this land became unorganized territory. North Carolina also ceded its claim to its western counties, but this was not officially accepted by Congress until 1790. New York ceded its claim on the Erie Triangle to the federal government. At this point in history, all of the states except for Georgia and Virginia were at their present-day borders, except for some of the minor issues mentioned above.
West Florida claimed a border further north than what the United States said it had. Its border had been 31° north when Spain ceded it to the United Kingdom. The British later moved its border north to 32°38′ latitude, but when Spanish Florida was ceded back to Spain in the Treaty of Paris, the British cited the original border at the 31st parallel north, but Spain continued to claim the higher border. Also, the borders at the northern area of the Maine District of Massachusetts and the area northwest of Lake Superior remained disputed.
- August 7, 1789
The United States Congress affirmed the organization of the Territory North West of the Ohio River, or Northwest Territory, under the terms of the Northwest Ordinance. Northwest Territory consisted of present-day Illinois, Indiana, Michigan, northeastern Minnesota, most of Ohio, and Wisconsin. The Northwest Territory had previously been organized under the Articles of Confederation on July 13, 1787, and was slightly modified under the new Constitution.
- April 2, 1790
- May 26, 1790
- March 4, 1791
The Vermont Republic, which had portions claimed by New York and New Hampshire and, while unrecognized by the United States, was a de facto independent country, was admitted as the 14th state, Vermont.
- September 9, 1791
- March 3, 1792
- June 1, 1792
- January 11, 1794
In the third Nootka Convention Spain surrenders its exclusive claim to the entire Pacific Coast and acknowledges the right of Britain or other powers to use unoccupied territory.
- October 27, 1795
- June 1, 1796
- April 7, 1798
Due to the Yazoo Land Fraud, an act was signed by President John Adams, authorizing him to appoint commissioners to negotiate with Georgia about ceding its western land. The act created Mississippi Territory in the region ceded by West Florida, corresponding to roughly the southern third of present-day Mississippi and Alabama except their panhandles, which were part of West Florida.
- July 4, 1800
Indiana Territory was formed from the western portion of Northwest Territory. It corresponded to present-day Illinois, Indiana, northeastern Minnesota, and Wisconsin, as well as the western half of the Lower Peninsula of Michigan and all but the eastern tip of the Upper Peninsula. Northwest Territory was left with only most of Ohio and the rest of Michigan.
- July 10, 1800
- October 1, 1800
The secret Third Treaty of San Ildefonso transferred the colony of Louisiana from Spain to France. Its boundaries were not specified and control was not actually transferred until the Louisiana Purchase.
- April 26, 1802
- March 1, 1803
- April 30, 1803
The Louisiana Purchase was made, expanding the United States west of the Mississippi River. The U.S. later had a dispute with Spain regarding whether France had included Spanish West Florida, located east of the Mississippi River, in the sale. West of the Mississippi, it was defined as the Mississippi Basin, whose extent was not known at the time and extended slightly north of the modern Canada-US border. It consisted of the whole of present-day Arkansas, Kansas, Iowa, Missouri, Nebraska, and Oklahoma, and portions of Colorado, Louisiana, Minnesota, Montana, New Mexico, North Dakota, South Dakota, Texas and Wyoming. It also included the southernmost portions of the present-day Canadian provinces of Alberta, Manitoba, and Saskatchewan.
- March 27, 1804
The unorganized land ceded by Georgia was added to Mississippi Territory, consisting of the whole of present-day Mississippi and Alabama, minus their panhandles which were still part of West Florida.
- October 1, 1804
The Louisiana Purchase was split into the District of Louisiana, which was temporarily under the authority of Indiana Territory, and the organized Territory of Orleans, which corresponded to part of present-day Louisiana with a small portion of Texas. The western border of Orleans Territory caused further conflict with New Spain, specifically over the region between the Sabine River on the west and the Arroyo Hondo (River) on the east, which became known as the Sabine Free State. This land was later confirmed as U.S. territory by the Adams-Onís Treaty of 1819.
- January 11, 1805
Michigan Territory was split from Indiana Territory, including the whole of the lower peninsula of present-day Michigan but only that eastern tip of the upper peninsula which was held by the Northwest Territory after Indiana Territory had been split from it.
- July 4, 1805
- March 1, 1809
Illinois Territory was split from Indiana Territory. Illinois Territory included present-day Illinois, northeastern Minnesota, and Wisconsin. Indiana Territory included the present-day borders of Indiana, with its western and eastern borders continuing northward; thus, it also included the central portion of the upper peninsula of Michigan, as well as Door Peninsula of present-day Wisconsin.
- April 1810
- October 27, 1810
By proclamation of President James Madison, the United States annexed the Baton Rouge and Mobile Districts of Spanish West Florida, declaring them to have been part of the Louisiana Purchase. One month earlier, these had declared independence from Spain as the Republic of West Florida. The U.S. Army seized control by threat of force in December after 90 days of independence as a country.
- April 30, 1812
- May 12, 1812
- June 4, 1812
- April 17, 1813
Republican Army of the North captured San Antonio, Texas, assassinated the governor Manuel María de Salcedo, proclaimed Texas an independent nation, and issued Texas's first constitution on this date. Spanish forces recaptured the province later that year and executed any Tejanos accused of having Republican tendencies. By 1820 fewer than 2000 Hispanic citizens remained in Spanish Texas.
- December 11, 1816
- March 3, 1817
- December 10, 1817
- October 20, 1818
The Treaty of 1818 established the 49th parallel north west of the Lake of the Woods as the border with British-held lands, and Oregon Country was established as a shared land between the United States and United Kingdom. Oregon Country consisted of most of present-day Idaho and Oregon, all of Washington, and a portion of Montana, as well as the southern part of the Canadian province of British Columbia. The treaty transferred the Red River Basin to the United States, consisting of northwestern Minnesota, northeastern North Dakota, and the northeastern tip of South Dakota.
- December 3, 1818
The southern portion of Illinois Territory was admitted as the 21st state, Illinois. The remainder was reassigned to Michigan Territory. The unorganized lands which had been a part of Indiana Territory prior to the admission of Indiana as a state were also assigned to Michigan Territory.
- March 2, 1819
- December 14, 1819
- March 16, 1820
- July 10, 1821
The Adams-Onís Treaty or Transcontinental Treaty came into effect, establishing a defined border between the United States and New Spain. The treaty ceded Spain's claims to Oregon Country to the United States and American claims to Texas to Spain; moved portions of present-day Colorado, Oklahoma, and Wyoming, and all of New Mexico and Texas, to New Spain; and all of Spanish Florida to the United States. The new borders intruded on Arkansaw Territory's Miller County, created on April 1, 1820, which dipped below the Red River and into land now ceded to Spain. However, the remoteness of the region caused no serious conflict with Spain.
- August 10, 1821
The southeastern corner of Missouri Territory was admitted as the 24th state, Missouri. The remainder became unorganized. Missouri did not include its northwestern triangle at this point, that being added later in the Platte Purchase.
- September 16, 1821
Ukase of 1821 attempts to forbid non-Russian ships from approaching the Northwest Coast. Only attempt at enforcement is seizure of the U.S. brig Pearl in 1822. U.S. reacts with the Monroe Doctrine in 1823.
- September 27, 1821
- March 30, 1822
East Florida and the portion of West Florida not already part of other states were combined and organized as Florida Territory, which corresponded to present-day Florida. Around this time, the official spelling of Arkansaw Territory became Arkansas Territory.
- November 15, 1824
- January 12, 1825
Russo-American Treaty of 1824 gave Russian claims south of parallel 54°40′ north to the United States. This and the Anglo-Russian Convention of 1825 leave Britain and the U.S. as the only claimants to Oregon Country. Russia retained Fort Ross, California until 1841.
- May 6, 1828
- June 30, 1834
- March 2, 1836
The Republic of Texas declared independence from Mexico, claiming a Rio Grande boundary encompassing present-day West Texas, the majority of New Mexico, and portions of Colorado, Kansas, and Wyoming. Actual control extended over approximately the eastern half of present-day Texas. Miller County in Arkansas Territory now intruded on the borders of Texas, and the people there began to take a Texian identity, leading to both governments having representatives from the county.
- June 15, 1836
- July 4, 1836
Wisconsin Territory was split off from Michigan Territory, consisting of present-day Wisconsin, Minnesota, Iowa, and eastern North and South Dakota. As an inducement to give up its claim over the Toledo Strip to Ohio, the whole of the present-day upper peninsula was assigned to Michigan Territory, giving it the present-day borders of Michigan.
- January 26, 1837
- March 28, 1837
- July 4, 1838
Iowa Territory was split off from Wisconsin Territory, consisting of present-day Iowa, western Minnesota, and eastern North Dakota and South Dakota, leaving Wisconsin Territory with northeastern Minnesota and Wisconsin.
- November 10, 1842
The Webster–Ashburton Treaty settled the border between the United States and lands held by the United Kingdom east of the Rocky Mountains, ending the disputes over the northern border of the state of Maine and northeastern border of Wisconsin Territory, which today resides in present day Minnesota.
- March 3, 1845
- December 29, 1845
The Republic of Texas was admitted as the 28th state, Texas. The United States Congress passed the joint resolution of annexation on March 1, 1845, but Texas did not agree to join the union for some time after. Although the annexation resolution avoided specifying Texas's boundaries, the U.S. inherited Texas's unenforced claims to South Texas, West Texas, over half of New Mexico, a third of Colorado, and small parts of Oklahoma, Kansas and Wyoming. With Texas joining the union, Arkansas finally gave up its claim on Miller County.
- June 18, 1846
The Oregon Treaty established the 49th parallel west of the Lake of the Woods as the continental border (so it did not include Vancouver Island) with the lands held by the United Kingdom. The sharing of Oregon Country ended, and the American portion becomes unorganized territory.
- August 15, 1846
U.S. Army of the West (1846) under Stephen Kearny captures New Mexico and claims it for the U.S.
He installs a U.S. military government of New Mexico under the Kearny Code and later a provisional government of New Mexico, subject to the federal government and not to Texas.
- December 28, 1846
- January 13, 1847
- March 13, 1847
The District of Columbia retroceded its land south of the Potomac River back to Virginia. Congress passed the retrocession act on July 9, 1846, and Virginia took possession of the land on this date.
- February 2, 1848
The Treaty of Guadalupe Hidalgo ended the Mexican-American War. Mexico ceded the Texas-claimed areas as well as a large area of land consisting of all of present-day California, Nevada, and Utah, most of Arizona, and portions of Colorado, New Mexico, and Wyoming.
- May 29, 1848
- August 14, 1848
- March 3, 1849
- September 9, 1850
The Compromise of 1850 divided the Mexican Cession and land claimed by Texas but ceded to the federal government in exchange for taking on its debts. The western portion was admitted as the 31st state, California, most of the rest was organized as Utah Territory and New Mexico Territory, and a small portion became unorganized land. New Mexico Territory consisted of most of present-day Arizona and New Mexico, as well as a southern portion of Colorado and the southern tip of Nevada. Utah Territory consisted of present-day Utah, most of Nevada, and portions of Colorado and Wyoming. A peculiarity appeared at this time, when a small strip of land north of Texas was not officially designated as part of any state or territory (Texas gave up this land due to a United States federal law based on the Missouri Compromise, which prohibited slavery above the 36°30' parallel of North latitude). This came to be called the Neutral Strip or "No Man's Land", which corresponds to the present-day panhandle of Oklahoma.
- March 2, 1853
Washington Territory was split from Oregon Territory, consisting of present-day Washington, northern Idaho, and the western tip of Montana, leaving Oregon Territory with all of Oregon, southern Idaho and a portion of Wyoming.
- December 30, 1853
The Gadsden Purchase added some land to New Mexico Territory, corresponding to the southernmost areas of present-day Arizona and New Mexico. With the purchase, the territorial extent and external borders of the present-day Contiguous United States are established (unless the San Juan Islands of present-day Washington state are included - see below).
- May 30, 1854
Kansas Territory and Nebraska Territory were organized; the remaining unorganized land colloquially became known as Indian Territory. Kansas Territory consisted of present-day Kansas and eastern Colorado. Nebraska Territory consisted of present-day Nebraska, and parts of Colorado, Montana, North Dakota, South Dakota, and Wyoming. Indian Territory corresponds to eastern Oklahoma.
- May 11, 1858
- February 14, 1859
- February 8, 1860
- January 29, 1861
- February 4, 1861
The CSA states evolution.
- February 28, 1861
Colorado Territory was organized from land taken from New Mexico, Utah, and Nebraska territories and unorganized territory previously part of Kansas Territory. It occupied present-day Colorado. Also, the eastern tip of the Washington Territory was transferred to Nebraska Territory.
- March 2, 1861
Dakota Territory was split from Nebraska Territory, and included the unorganized land left over from Minnesota Territory. Dakota Territory consisted of both present-day North and South Dakota, as well as most of Montana and northern Wyoming. Nebraska Territory consisted of all of Nebraska and southeastern Wyoming. Nevada Territory was split from Utah Territory, corresponding to northwestern present-day Nevada; the eastern border was the 39th meridian west of Washington, D.C.
- August 1, 1861
The Confederacy established Arizona Territory (CSA) in the southern half of the Union's New Mexico Territory. It would be organized on February 14, 1862. It corresponded to the southern halves of present-day Arizona and New Mexico.
- July 14, 1862
Due to its nature as a mining and grazing area, land started to be added to Nevada Territory to accommodate these activities. Its eastern border was moved eastward from the 39th meridian west from Washington, to the 38th meridian west from Washington, transferring the land from Utah Territory.
- February 24, 1863
The Union created its own Arizona Territory, splitting it off from New Mexico Territory, making both territories correspond to their present-day states, except for Arizona Territory including the southern tip of present-day Nevada.
- March 4, 1863
Idaho Territory was created from portions of Washington, Dakota, and Nebraska Territories, consisting of present-day Idaho, Montana, and most of Wyoming. Nebraska and Washington Territories were left corresponding to their present-day counterparts.
- June 20, 1863
The counties of northwestern Virginia (whose population had opposed secession from the Union and established a pro-Union state government) were split off and were admitted as the 35th state, West Virginia. The new state had been mostly under Union control since late 1861, but is not recognized by the Confederate and state governments in Richmond.
- May 26, 1864
Montana Territory was split from Idaho Territory, which also had some land transferred to Dakota Territory. Montana Territory corresponded to present-day Montana, Idaho Territory consisted of Idaho and western Wyoming, and Dakota Territory included both North and South Dakota, and most of Wyoming.
- October 31, 1864
- April 9, 1865
The CSA states evolution.
- May 5, 1866
- January 18, 1867
- March 1, 1867
- October 11, 1867
- July 25, 1868
- October 21, 1872
- August 1, 1876
- March 28, 1882
- May 17, 1884
- November 2, 1889
- November 8, 1889
- November 11, 1889
Washington Territory was admitted as the 42nd state, Washington.
- May 2, 1890
- July 3, 1890
- July 10, 1890
- July 4, 1894
- January 4, 1896
- May 4, 1896
- August 12, 1898
- June 14, 1900
- October 20, 1903
The Alaska boundary dispute is resolved by arbitration, generally favoring the American claim.
- November 16, 1907
- January 6, 1912
- February 14, 1912
- August 24, 1912
- March 28, 1921
- January 3, 1959
Alaska Territory was admitted as the 49th state, Alaska.
- August 21, 1959
Hawaii Territory was admitted as the 50th state, Hawaii, resulting in the present-day situation of the United States. The statehood act specifically excluded Palmyra Atoll from the new state; it thus became unorganized land. Since it had been incorporated as part of the Hawaii Territory, Palmyra Atoll became the only incorporated territory left in the United States.
- January 14, 1963
The Chamizal Dispute with Mexico over about 600 acres (2.4 km2) on the U.S.-Mexico border between El Paso, Texas, and Ciudad Juárez, Chihuahua is resolved. It was caused by differences between the bed of the Rio Grande as surveyed in 1852 and the channel of the river in 1895.
The small town of Rio Rico, Texas, was ceded to Mexico in the Boundary Treaty of 1970. The handover officially took place in 1977, and the town was added to the Mexican state of Tamaulipas, of which it had long considered itself a part. See Mexican Boundary Exchanges.
- Geography of the United States
- Historic regions of the United States
- List of U.S. states by date of statehood
- National Atlas of the United States
- Territorial evolution of U.S. states:
- Territorial evolution of Arizona
- Territorial evolution of California
- Territorial evolution of Colorado
- Territorial evolution of Idaho
- Territorial evolution of Montana
- Territorial evolution of Nevada
- Territorial evolution of New Mexico
- Territorial evolution of North Dakota
- Territorial evolution of Oregon
- Territorial evolution of South Dakota
- Territorial evolution of Utah
- Territorial evolution of Washington
- Territorial evolution of Wyoming
- United States territorial acquisitions
- Stein, Mark, How the States Got Their Shapes, New York : Smithsonian Books/Collins, 2008. ISBN 978-0-06-143138-8
- States of the United States from Statoids.com.
- The 50 State Quarters Program at the United States Mint, listing dates of statehood.
- insular areas.
- International the original on 2007-12-23)
- Manifest Destiny Interactive version of this article.