The treasury note is thought to be only one of two in existence. The other is on display at the Smithsonian American History Museum in Washington.
Heritage Auctions said the $2.585 million set a record for a piece of paper currency.
It was put on the auction block in Schaumburg, Ill., Saturday. The bill was last sold at auction in 1944, when it sold for barely more than its nominal worth -- $1,350.
Among its previous owners is Amon G. Carter Jr., the collector and former publisher of the Forth Worth (Texas) Star-Telegram.