Voting was 50 per cent from on-line US supporters and 50 percent from media and US Soccer representatives.
It was the second time that Dempsey has taken the award, also getting the nod in 2007. The 28-year-old US midfielder has netted six goals so far this season for Fulham in the English Premier League. Dempsey now ranks as the highest-scoring American in Premier League history, passing Brian McBride's 36 goals in early December.
Dempsey scored a tournament-best three goals in last year's CONCACAF Gold Cup but the Americans lost to Mexico in the final, setting the stage for the sacking of coach Bob Bradley and the signing of new coach Jurgen Klinsmann.
"I would like to thank the fans for voting me Athlete of the Year," Dempsey said. "It always feels good to be recognized for doing a good job at something you love to do. I would like to thank my teammates and coaching staff for all their hard work and hopefully we can have a better 2012."
Only four-time winner Landon Donovan and three-time winner Kasey Keller have taken the US Soccer men's prize more often than Dempsey since the award was created in 1984.
Wambach captured the women's award for the fifth time and second year in a row, matching the record all-time total of Mia Hamm. She scored goals in the last four US matches of the Women's World Cup, which the Americans lost on penalties to Japan in the final.
"I can always say very safely that it's a team award," Wambach said. "Germany was amazing. We as a team went over there and did some amazing things."