Schmitt swam the anchor leg as the United States set a world record with a time of 3:52.05. Australia was second in 3:54.02 and Japan placed third in 3:55.73. It marked the first gold in the 400 IM relay for the U.S. women since 2000.
Schmitt concluded the London Games going 5-for-5 on medals in her events. She picked up the gold on Wednesday, another gold in the 200-meter freestyle, a silver in the 400-meter freestyle and a bronze on the 4x100-meter freestyle relay.
A rising senior from Canton, Mich., Schmitt now has six medals, including a bronze at the 2008 Games, and that is the highest total in Georgia history.
Saturday marked the final day of swimming at the London Olympics.