The tally stands as the highest number of COVID-19 deaths reported by any nation, followed by Russia, Brazil and India with more than 1.8 million deaths combined.
Propelled in part by the wildly contagious Omicron variant, the US death toll from COVID-19 hit 900,000 on Friday, less than two months after eclipsing 800,000.
The two-year total, as compiled by Johns Hopkins University, is greater than the population of Indianapolis, San Francisco, or Charlotte, North Carolina.
The milestone comes more than 13 months into a vaccination drive that has been beset by misinformation and political and legal strife, though the shots have proved safe and highly effective at preventing serious illness and death.
"It is an astronomically high number. If you had told most Americans two years ago as this pandemic was getting going that 900,000 Americans would die over the next few years, I think most people would not have believed it," said Dr Ashish K Jha, dean of the Brown University School of Public Health.
He lamented that most of the deaths happened after vaccines gained authorisation.
"We got the medical science right. We failed on the social science. We failed on how to help people get vaccinated, to combat disinformation, to not politicise this," Jha said.
President Joe Biden lamented the milestone on Friday night: "After nearly two years, I know that the emotional, physical, and psychological weight of this pandemic has been incredibly difficult to bear."
He again urged Americans to get vaccinations and booster shots.
Just 64 per cent of the population is fully vaccinated, or about 212 million Americans, according to the Centers for Disease Control and Prevention.
Nor is COVID-19 finished with the United States: Jha said the US could reach one million deaths by April.
The latest bleak milestone came as Omicron is loosening its grip on the country.
Daily cases have plunged by almost 500,000 since mid-January, when they hit a record peak of more than 800,000. Also, the number of Americans in the hospital with COVID-19 has declined 15 per cent since mid-January to about 124,000.
Deaths are still running high at more than 2400 per day on average, the most since last winter. And they are rising in at least 35 states, reflecting the lag between when victims become infected and when they succumb.
Still, health officials have expressed hope the worst of Omicron is coming to an end. While they caution that things could still go bad again and dangerous new variants could emerge, some places are already talking about easing precautions.
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