On what date did U.S. sovereignty over Alaska become effective after the Alaska Purchase?

U.S. sovereignty over Alaska became effective on October 18, 1867, after the Alaska Purchase.

The United States had agreed to buy Alaska from the Russian Empire for $7.2 million. The treaty was signed on March 30, 1867, and the U.S. Senate ratified it on May 15, but the formal transfer of sovereignty occurred months later.

The transfer ceremony took place in Sitka. Russian soldiers lowered their flag while American soldiers raised the United States flag, accompanied by artillery. The date remains commemorated in Alaska as Alaska Day.

Many Americans initially mocked the deal as “Seward’s Folly,” referring to Secretary of State William H. Seward. Gold discoveries and later recognition of Alaska’s immense natural resources helped transform public opinion about the purchase.