The state reported Montana added 37 new laboratory-confirmed coronavirus cases Thursday, the largest single-day rise reported to date.
The previous peak was 35 cases on March 26, about two weeks after Montana's first cases.
The number of cases added daily as been climbing over the last couple of weeks as the state opens up more.
There are 210 active cases and 15 hospitalizations. The state has 803 total cases with 572 recovered.
Yellowstone County added 10 cases Thursday. Gallatin County added seven, Dawson added six and Missoula added four.
Big Horn, Flathead and Butte-Silver Bow counties all added two cases. Carbon, Custer and Ravalli counties each added a case. Granite County reported its first case Thursday.
A stay-at-home order lifted April 26, with some businesses allowed to open the following day. In the following weeks, gyms, theaters and bowling alleys returned. By June 1, Montana entered its second phase of reopening, with greater capacity at bars and restaurants and the expiration of a 14-day travel quarantine.
In a press conference Wednesday, state health officials said many of the new clusters in Montana can be tied to people in group settings, such as traveling together in a vehicle or workplaces.
Gov. Steve Bullock has encouraged people to wear masks in situations that do not allow for social distancing, but stopped short of ordering people to do so. The Centers for Disease Control and Prevention has said wearing masks slows the transmission of the disease.
Testing has also increased in Montana, with the state reporting 3,266 new tests processed between Wednesday and Thursday. Bullock has set an ambitious testing goal of 60,000 a month; the state reached just over 78,300 total tests Thursday.
Communities around the state are holding snapshot testing events, as are so-called destination communities tied to heavy visitor activity. Bullock said Wednesday about 8% of cases in Montana are tied to travel.
The Red Cross held a blood drive at Fort Harrison in Helena on Thursday and will test the blood donated for coronavirus antibodies. The organization is testing all donated blood for antibodies, sending Montana samples to a laboratory in Arizona.
Diane Wright, executive director of the Red Cross in Montana, said the organization has been testing donated blood for antibodies since June 15. People are notified of their results within seven to 10 days over the Red Cross' blood donation smartphone app.
Wright said the organization has seen an increase in appointments to donate recently, as well as higher need for blood as hospitals resume elective surgeries.
Antibody testing can determine if a person has ever been exposed to the virus.
Master Sgt. Michael Touchette was giving blood Thursday because he frequently donates blood and wasn't aware of the antibody testing, but said he'd be curious about the results. He was sick with lingering respiratory symptoms in January this year, before the coronavirus had entered the awareness of most Montanans.