New cases surged to 3,266 from the 738 reported Monday, according to the state's health department. That's the highest one-day number since September 19.
DeSantis lifted restrictions on bars and residents Friday, and scenes of crowded bars and restaurants played out around the state over the weekend.
Until recently a coronavirus hotspot, Florida's cases had been falling, and the state is among only seven with at least a 10% reduction in new cases in the week ending Monday compared to the previous seven days.
Arizona, Georgia, Maryland, Rhode Island, Texas and Virginia are the other six states with a decline in new cases in the past week.
Florida has reported 704,568 cases in total.
In Wisconsin, Covid-19-related hospitalizations have almost doubled since September 18, according to the Wisconsin Hospital Association, with "multiple hospitals" nearing capacity.
Gov. Tony Evers declared a "a new public health emergency due to campus outbreaks" on September 22, and the WHA sent Evers a letter "requesting additional and immediate policy steps be taken to help hospitals preserve access to care during this troubling new phase of the pandemic."
"Over the past week, the rate of COVID-19 patients hospitalized per day in Wisconsin has rapidly increased from 362 per day on September 19, to 528 per day on September 24 -- a new record that exceeds the previous peak of 446 hospitalizations per day on April 9," the letter dated September 25 reads.
"Multiple hospitals in the Fox Valley, Northeast, and North Central HERC regions are now reporting they are nearing capacity."
Dr. Paul Casey, medical director of the emergency department at Bellin Hospital, made a public plea on Facebook for Wisconsinites to take the pandemic more seriously.
"I can't speak to other areas in the state, but in Brown County, we're in deep trouble," Casey told CNN affiliate WBAY.
Evers cautioned Tuesday that the virus is "not slowing down, it's picking up speed."
"If we're going to get this virus under control, then wearing a mask is the absolute least we need you to do," Evers said at a news conference. "It isn't safe. This virus is real, and it's devastating our communities."
In less than nine months, the death toll jumped from one coronavirus-related death -- in Wuhan, China, on January 9 -- to 1,004,482 Tuesday afternoon, according to data from Johns Hopkins University. The US has been hit hard by the virus, with almost 7.2 million reported infections and more than 205,000 deaths.
With recent spikes in US cases, health experts warn things could soon get worse.
Only 20 states are holding steady when it comes to the average of daily new cases compared to last week, while 23 are reporting increases: Alabama, Alaska, Colorado, Idaho, Indiana, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Nevada, New Jersey, New Mexico, North Carolina, North Dakota, Oregon, South Carolina, South Dakota, Utah, Vermont, Washington, Wisconsin and Wyoming.
Fall and winter promise to drive more people indoors and bring about flu season, and experts say Americans need to be consistent in following guidelines. Mask wearing, social distancing and avoiding large crowds will be key, experts say, along with authorities increasing testing as infections surge again.
Worldwide, the US ranks No. 1 in the total number of reported deaths and fifth per 100,000 people.
Johns Hopkins' tally shows the US, Brazil, India and Mexico account for more than 50% of coronavirus deaths.
Biotechnology company Moderna and the National Institutes of Health expanded an early-phase trial of their vaccine candidate and found the vaccine safely brought about an immune response in older adults.
"The immune response to many other vaccines has been shown to decrease with increasing age. Thus, the testing of SARS-CoV-2 vaccine candidates in older populations is of paramount importance, since these persons account for the majority of serious Covid-19 cases and associated deaths," the NIH-led researchers wrote in the study, published in the New England Journal of Medicine on Tuesday. SARS-CoV-2 is the name of the coronavirus that causes Covid-19.
The Phase 1 clinical trial expansion included 40 participants who were 56 and older, who were given two doses of either 25 micrograms or 100 micrograms of vaccine, 28 days apart. The immune reaction was stronger in the group that got the larger dosage.
Adverse side effects were mostly mild or moderate, according to the researchers.
As for treatment, early results of tests of Regeneron's antibody cocktail in coronavirus patients seemed to reduce virus levels and improved patients' symptoms, the biotechnology company said.
The results involve only 275 patients but appear "very promising," Dr. Jeanne Marrazzo, the director of the division of infectious diseases at the University of Alabama at Birmingham, told CNN.
The greatest improvements were seen in patients who hadn't already mounted a natural response to the infection, the company said.
The data has not yet been peer reviewed.
As trends vary across the US, some local leaders are stepping back toward normal while others are clamping down on efforts to combat the virus' spread.
Chicago bars, restaurants, gyms and personal services will be allowed to expand service Thursday because of "sufficient progress in the fight against Covid-19," Chicago Mayor Lori Lightfoot said Monday.
"Over the past six months, we have asked so much of our business community, but each time, our businesses have stepped up to the plate," she said in a news release. "This next step in our reopening is good news for business owners as well as the communities they serve and the thousands of residents that work for them."
Hard-hit California is seeing coronavirus positivity rate, hospitalizations and new cases trending downward, Gov. Gavin Newsom said Monday, but he cautioned the numbers could pick back up if residents don't remain vigilant.
Meanwhile, New York will release guidance this week to reopen "Covid-safe" homeless shelters, noting a rise in cases among homeless encampments, Gov. Andrew Cuomo said. Cases are also rising at an "alarming" rate in parts of Brooklyn and Queens, the New York City Health Department said.
New Jersey is set to receive 2.6 million rapid coronavirus tests from the federal government to help fight spikes in cases.
CORRECTION: This story has been updated to reflect the number of months between the first and 1 millionth global death from Covid-19. It took less than nine months to reach that milestone.