Professor Michael McDonald at George Mason University this morning reported that his preliminary estimate was that voter turnout in yesterday's election was 64.1%, of eligible voters (not registered voters or voting age population alone), topping the 1960 voter turnout rate of 63.8%. If his estimate holds up, this will mark the highest voter turnout since the 65.7% turnout rate in 1908.
However, he now has revised his estimate downwards and we won't have final numbers available for several days. His latest post reported that turnout may end up being 62.3%, or 132.8 million votes cast. He'll be tracking exactly many absentee ballots and provisional ballots are yet to be counted.
Professor McDonald's preliminary numbers are posted on his website.