What was the deadliest day in US history?

If you think of the deadliest day in the United States' History, your mind is probably drawn to the terrorist attacks of September 11, the calamity that followed Japan's strike on Pearl Harbor or perhaps a battle from the Civil War. Or maybe you think of more recent days during the COVID-19 pandemic. 

The answer to the question of what was the deadliest day, it turns out, isn't straightforward. But when you take the death rate into account, it's likely none of the events mentioned above.

To put contemporary U.S. deaths in perspective, before COVID-19 began circulating in late 2019, approximately 7,700 people died every day in the U.S. for a multitude of different reasons, including things like car accidents and heart disease, said J. David Hacker, a demographic historian at the University of Minnesota.

Related: What's the deadliest day of the week?

The deadliest day in America's History is hard to pinpoint because, for one thing, America's population has grown considerably, from a mere 4 million in 1790 to in excess of 332 million today, Hacker said. So, comparing the absolute number of deaths from yesteryear with today is like comparing apples with oranges.

"Of course there are more overall deaths in a typical day today than there were in 1790, despite the fact that the death rate — deaths divided by the population — was undoubtedly much higher in 1790," Hacker told Live Science. But even if we decide that the death rate is the fairer way to make comparisons across the centuries, finding an answer to the "deadliest day' question is still more complicated than you might think.

"The deadliest day comparisons I've seen rely on different measures," Hacker said. If we're looking at a single attack or event, do we discount the people who also died on that day, but from other causes? Or do we include them? There's not much of a consensus among historians, and, on top of that, death records nationwide from 1776 to now are lacking, Hacker said.