Initial estimates say the crowd at Monday's inaugural was at least one million people.
That's down from the 1.8 million who came out to see President Obama sworn in the first time.
But even so, a turnout of a million people puts Obama's second inaugural among the biggest ever.
It's more than double the 400,000 who turned out to see George W Bush's second inaugural address, and it tops the 800,000 who watched Bill Clinton sworn in the first time.
Before Obama, the previous record was 1.2 million people who came out for Lyndon Johnson's inaugural in 1965.