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ThePlatte Purchase was a land acquisition in 1836 by theUnited States government fromAmerican Indian tribes of the region. It comprised lands along the east bank of theMissouri River and added 3,149 square miles (8,156 km²) to the northwest corner of the state ofMissouri.

This expansion of the slave state of Missouri was in violation of theMissouri Compromise of 1820, which prohibited the extension of slavery in the formerLouisiana Territory north of the parallel 36°30′ north, except within the boundaries of the state of Missouri, as defined at the time of the adoption of the Missouri Compromise.^[1] The area acquired was almost as large as the states ofDelaware andRhode Island combined, and extended Missouri westward along the river.St. Joseph, one of the main river ports of departure for the westward migration ofAmerican pioneers, was located in the new acquisition.

This territorial expansion significantly altered the state's borders and extended slavery north of the Missouri Compromise line. The newly acquired counties would later play important roles in both westward expansion and the regional politics of pre–Civil War Missouri.^[2]

The region of the Platte Purchase includes the following modern counties within its bounds:Andrew,Atchison,Buchanan,Holt,Nodaway,Platte, and a small portion ofWorth. It also includes what are now the northwest suburbs ofKansas City, a small area of Kansas City proper, the cities ofSt. Joseph andMaryville, Missouri, as well asKansas City International Airport and almost all of Missouri's portion ofInterstate 29, save the small portion which runs concurrently withInterstate 35 inClay County.

When Missouri entered the Union, its western border was established as

"a meridian line passing through the middle of the mouth of theKansas river, where the same empties into the Missouri river, thence, from the point aforesaid north, along the said meridian line, to the intersection of the parallel of latitude which passes through the rapids of the river Des Moines, making the said line correspond with the Indian boundary line."^[3]

The purchase extended Missouri's western border north of the Kansas River east along the Missouri River to 95°46′ west longitude.

Less than a year after theIndian Removal Act of 1830, by which the US was authorized to remove the Native American population, the Missouri General Assembly was petitioning Congress to more clearly define the border on the northwest corner of the state. The Legislature noted the boundary was not clear, and that the land was not surveyed, thus leading to settlers encroaching on the lands. The most spectacular example of encroachment wasJoseph Robidoux, who had been operating anAmerican Fur Company trading post atSt. Joseph, Missouri since 1826.

On January 27, 1835, SenatorLewis F. Linn wrote John Dougherty, an Indian agent, to inquire about acquiring the land. Dougherty agreed, noting that the territory was preventing access to Missouri River shipping by Missouri residents east of the purchase line. According to an early 20th-century historian, Dougherty's reputation among the Native Americans was that of the "Controller ofFire-water" from the Missouri River to the Columbia River.^[4]

The first tribes to give up their land were thePotawatomi, who ceded their land in theTreaty of Chicago. They agreed to this in 1833 but the treaty wasn't finalized until 1835. The Potawatomi (about 1,000 to 2,000) moved north to a reservation inPottawattamie County, Iowa (Council Bluffs, Iowa).^[5] They moved again 1837–1838 in thePotawatomi Trail of Death toOsawatomie, Kansas.

The formal application came in the summer of 1835 at a meeting on the Dawes farm nearLiberty, Missouri. Andrew S. Hughes, the US Indian agent for the Sauk and Meskwaki peoples, presided over a meeting of Missouri residents who formally asked Congress to acquire the land. Missouri senatorThomas Hart Benton introduced a bill to acquire the land and it was approved with little opposition in June 1836.^[4]

An agreement was reached on September 17, 1836, with the chiefsMahaska andNo Heart of theIoway tribe and leaders of the combinedSauk andMeskwaki tribes in a ceremony atFort Leavenworth, Kansas. It was presided byWilliam Clark, the Superintendent of Indian Affairs, who was based in St. Louis.^[6] (He was one of the leaders of theLewis and Clark Expedition.) Noted diplomatJeffrey Deroine, a formerly enslaved man, served as an interpreter for this treaty.^[7]

TheSenate approved the treaty on February 15, 1837. On March 28, 1837, PresidentMartin Van Buren issued a proclamation supporting the annexation. In October 1837, the Missouri General Assembly accepted the land and placed it all initially in the newly created Platte County.^[4][8]

This addition increased the land area of what was already the largest state in the Union at the time (about 66,500 square miles (172,000 km²) to Virginia's 65,000 square miles, which then included West Virginia).^[9] The acquisition challenged theMissouri Compromise of 1820 by expanding slavery into free territory north of the southern Missouri border with Arkansas (Parallel 36°30′ north), and the Indian Removal Act. It required a second relocation of tribes who had just been moved "permanently" west of the Missouri border, as part of the forcedIndian removal policy of ethnic cleansing from lands wanted by whites.^[4]

The tribes were paid $7,500 for their land. The U.S. government was "to provide agricultural implements, furnish livestock", and a host of other small items. The tribes agreed to move to reservations west of the Missouri River in what was to becomeKansas andNebraska. Furthermore, the U.S. government was to "build five comfortable houses for each tribe, break up 200 acres (0.8 km²) of land, fence 200 acres (0.8 km²) of land, furnish a farmer, blacksmith, teacher, interpreter."^[6] The reservations are today known as theIowa Reservation and theSac and Fox Reservation. The tribes gave up 3.1 thousand square miles of land for reservations of 29 square miles combined (26 for the Sac and Fox and 3 for the Ioway).

Michigan entered the Union on July 4, 1836. By the time the Platte Purchase was finalized, Missouri remained the second biggest state.

The U.S. Government set up aUnited States General Land Office inPlattsburg, Missouri to handle the settlement. Much of the land was dispensed asmilitary land warrants to veterans of theWar of 1812 (and laterMexican–American War). Under the terms of the program, which was expanded in 1855, the 160-acre land grants could be given to military descendants and those grants could be sold.^[10][11]

Initial settlement was concentrated in theTown of Barry in south Platte County. Almost overnight, Platte County became the second-largest county in the state, andWeston, Missouri ("West Town") was second only toSt. Louis, Missouri in the state. St. Joseph would subsequently become the second-largest city in the state in the early settlement days. Since the purchase opened up a new slave area, the area was settled primarily by slaveholders from the Upper South: Virginia, Tennessee and Kentucky. They brought enslaved African Americans with them or purchased them at slave markets, to work such Southern commodity crops as the labor-intensivehemp andtobacco. These were grown in the southern portion of the purchase, where farms and plantations had access to the Missouri River for shipping to market. The northern portion of the purchase attracted fewer Southerners and slaveholding was rare.^[12]

Today the Platte Purchase area is among the most rural areas in Missouri. St. Joseph andMaryville, Missouri are the only communities totally within the purchase area that have populations greater than 10,000.Kansas City, Missouri has influenced the area, expanding its boundaries into southern Platte County.

A list of counties in the Platte Purchase region of Missouri including 2024 population estimates.^[13]
†Partially located outside of region

^α A portion of Congressional Townships 65, 66, and 67, Range 33 was originally part of Nodaway County^[14] and was later ceded to Worth County^[15]

A list of populated places in the Platte Purchase region of Missouri with2020 US census populations.^[16]

†County seat
††Partly outside Platte Purchase region

^α This settlement is within the original Platte Purchase boundary despite being in a county that is mostly excluded from the Platte Purchase.^[17]

• Historic regions of the United States
• Ioway Reservation
• Sac and Fox Reservation

• Kansas Historical Society history
• Nativeweb history including the treaty

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