On March 30, 1867, U.S. Secretary of State William H. Seward paid Russia $7.2 million for the 586,412-square mile territory of Alaska.
Russia set up a presence in Alaska in the 18th century, when Danish explorer Vitus Bering, with the backing of Russian Czar Peter the Great, surveyed the region. The territory was wild and inhospitable, but it was rich in natural resources, attracting Russian explorers and traders.
Russia did not have the money to establish permanent settlements, however, and its position was further weakened by their defeat in the Crimean War. By the mid-19th century, it was looking to sell off the land.
It offered Alaska to the United States, which was in the midst of a steady march westward, in 1859, but the threat of Civil War put off the sale. After the war, Secretary of State William Seward, a strong proponent of expansion, reopened talks with Russia, and agreed on March 30, 1867, to buy Alaska for $7.2 million, less than 2 cents per acre.
Many in the U.S. criticized Seward’s purchase. “Critics attacked him for the secrecy surrounding the deal with Russia, which came to be known as ‘Seward’s folly,’” writes the Library of Congress. “They mocked his willingness to spend so much on ‘Seward’s icebox’ or President Andrew Johnson’s ‘polar bear garden.’”
The Senate passed the treaty to buy Alaska by just one vote. The Alaskan territory was officially transferred to the U.S. on Oct. 18, 1867.
The above was here.
Wikipedia has more on the purchase here with this photo of the original check: