NBC says Sunday's Democratic debate was the third-most watched Democratic debate in history.
The network said Monday that Sunday's debate was watched by more than 12.5 million viewers, including 10.2 million who watched it live on NBC.
NBC says Sunday's debate drew more young viewers than the two previous broadcast debates.
Nearly 1.2 million viewers streamed the event live online, NBC says.
The Democratic National Committee-sanctioned event, hosted by the Congressional Black Caucus Institute, took place at the Gaillard Center in Charleston, South Carolina.
Democratic front-runners Hillary Clinton and Bernie Sanders, and former Maryland Gov. Martin O'Malley faced off in the debate — the last before voters in Iowa head to the polls for the leadoff caucus.