Olivia Culpo, 20, of Rhode Island, donned the coveted tiara Wednesday night.
She teared up as other contestants placed the crown on her head during the televised event in Las Vegas.
"What an honor! This night was a dream come true. Thank you everyone for your support tonight!! USA finally did it," Culpo posted on her official Twitter page later.
Culpo beat out 88 other contestants. Miss Philippines, Janine Tugonon, came in second.
Culpo won the Miss USA crown in June in part by emphasizing the importance of music education. A cellist for 13 years, Culpo has performed at Boston Symphony Hall and Carnegie Hall in New York City.
An American had not won the beauty pageant since 1997, according to organizers.
Last year's winner was Leila Lopes of Angola.xmoentertainment.blogspot.com