The winner - who may not be determined for days - will lead a nation strained by a pandemic that has killed more than 231,000 people and left millions more jobless, racial tensions and political polarization that has only worsened during a vitriolic campaign.
The ballots, which were mailed in, deposited in drop boxes or cast at polling stations ahead of Tuesday, represent more than 72 percent of the total number of ballots cast in the 2016.
The Republican Trump trails Biden in national opinion polls ahead of Tuesday's Election Day.
Trump will wrap up his campaign in Grand Rapids, Michigan, the same place he concluded his 2016 presidential run with a post-midnight rally on Election Day.
According to the tally from the US Elections Project, it which shows a record-breaking pace that could lead to the highest voter turnout in percentage terms in mote then a century.
Currency options investors are increasingly betting that Democratic challenger Joe Biden will conclusively defeat President Donald Trump, given his lead in prediction markets and national polls.