Around 136 million people voted four years ago.
Almost 70 million people voted early this year, a record figure that surpassed the 58 million mail-in or in-person early votes cast in 2016.
Figures shared by the US Elections Project appear to give Democrats the advantage on election day, leaving Republican President Donald Trump reliant on votes cast on Tuesday.
A majority of mail-in votes were cast by Democrats, figures collected from states that report party data reveals, while Republicans preferred to vote in-person.
"Time is starting to run short such that Republicans will need to rely heavily on Election Day vote, which has traditionally been a strong day of voting for Republicans in recent elections," US Elections Project director Michael McDonald said in a statement.
However, Democrats' tendency towards early voting could benefit their Republican rivals on election day.
"It should benefit Republicans who are trying to vote on election day that the Democrats have done them this favour of not standing in line in front of them," McDonald said.
Battleground states have witnessed a particular surge in early voting this year.
Texans have cast nearly 8 million early votes as of Tuesday this week, a figure that constitutes 86.9 percent of the state's total turnout in 2016.
Florida has also seen high-levels of early voting, with more than 6.4 million having cast their ballots so far. President Donald Trump voted early in the state on Saturday, casting his ballot in person.
Democrats currently hold an advantage of 7 percent in the key swing state, although that number has steadily decreased in the lead-up to election day.
"There's no way practically for Trump to get elected without Florida," Dr Larry Sabato of the University of Virginia's Center for Politics told The Guardian.
"If he loses there it will be obvious he's going to lose... If Biden loses Florida, though, it is not the end for him.
"The problem with losing Florida is it is an indication that you're likely not to do well in other states – we're talking about Georgia, North Carolina, even parts of the midwest," Sabato added.
Such figures promise a record-breaking turnout on Tuesday.
Voter turnout has hovered between 50 and 55 percent since the 1970s. It has not surpassed 62 percent since 1908, when more than 65 percent of eligible voters took part in the election.
While the high early voting figures represent the intensity of interest in the battle between President Trump and former Vice President Joe Biden, they also point to concerns over the spread of Covid-19.
The US has been the country worst affected by the pandemic, with around 227,000 dead and nearly nine million cases reported.
Follow us on [Facebook](https://en-gb.facebook.com/AlAraby.en/), [Twitter](https://twitter.com/TheewArab?refrc=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor) and [Instagram](https://www.instagram.com/thenewarab/?hl=en) to stay connected