The Louisiana Purchase was the acquisition of territory by the United States for 2,140,000 sq km of French territory in 1803. The cost was $11,250,000 (USD) also the cancellation of debts worth $3,750,000 (USD). Even at 3 cents an acre the United States could barely afford it and needed to borrow money. Including interest, the U.S. finally paid $23,213,568 (USD) for the Louisiana territory. France had just retaken control of the territory from Spain.
The land purchased as seen in the map above contained all of present-day Arkansas, Missouri, Iowa, Oklahoma, Kansas, Nebraska, parts of Minnesota that were south of the Mississippi River, most of North Dakota, nearly all of South Dakota, northeastern New Mexico, northern Texas, the portions of Montana, Wyoming, and Colorado east of the Continental Divide, and Louisiana on both sides of the Mississippi River, including the city of New Orleans.
In addition, the Purchase contained small portions of land that would eventually become part of the Canadian provinces of Alberta and Saskatchewan. The land included in the purchase comprises almost a quarter of the territory of the United States today. The purchase was an important moment in the presidency of Thomas Jefferson.
In the map above you can see the highlighted parts of what states where purchased. What you will notice is that the territory boundaries would become eastern state borders for the states of Iowa, Missouri and Arkansas.