Pritzker made the announcement after watching key COVID indicators going up - and after seeing so many school districts across the state deciding to make masking optional.
"Far too few school districts have chosen to follow the federal Centers for Disease Control's prescriptions for keeping students and staff safe, though I want to commend the districts in Edwardsville, Champaign, Peoria, Springfield, Elgin, Chicago and others for already doing the right thing for their students," Pritzker said. "Given the CDC's strong recommendation, I had hoped that a statewide school mask requirement wouldn't be necessary, but it is."
The goal to keep schools open and prevent COVID outbreaks, but the mandate extends beyond the classroom.
"Face coverings will be required for all indoor recreation, whereas outdoors, where transmission risks and rates are lower, athletes and coaches will not be required to mask," Pritzker said.
WATCH | Gov. Pritzker announces school mask mandate
The decision is being praised by school mask advocates, and criticized by those favoring choice.
"I think he didn't want to take the responsibility and accountability for this to begin with, because he didn't want the blowback," said Ronak Maisuria, a parent in Wheaton Warrenville District 200. "I give him credit for finally issuing a mandate, but he should have done it from the beginning."
"My position is, it's the parents' choice," said Meredith Darbyshire, the parent of two children in Glen Ellyn District 89. "And I believe that it should be optional, and it should be left up to the parents to make that decision for their family and what is best for their children."
The state's top doctor saying the percentage of COVID cases in young people under 20 has more than doubled since January. Hospitalizations have tripled in that time.
"There is an abundance of epidemiological evidence supports community masking to reduce the spread of the virus," said Dr. Ngozi Ezike.
WATCH: Political analyst weighs in on Illinois school mask mandate
Pritzker also announced that effective Oct. 4, vaccines will be mandated for state employees who work in in congregate settings, including veterans' homes, long-term care facilities, correctional facilities, developmental centers and psychiatric hospitals. The governor also is mandating masks in all long-term care facilities.
"They run the risk of carrying the virus in to work with them, then it's the residents who end up seriously sick or hospitalized or worse," Pritzker said. "It's a breach of safety, it's fundamentally wrong and in Illinois it's going to stop."
Republican leaders criticized the mandate, saying the decision should be left up to local officials and parents. They also criticized him for not including lawmakers in the action.
"People should go get vaccinated," Pritzker said, pounding the podium for emphasis. "That is the most important thing you can do to keep yourself, your community, your school safe, we hope that people will take advantage of that. That will reduce the need to have masks."
In a statement AFSCME Local 31, which represents state workers, said it stand ready to bargain with the Pritzker administration over the vaccine mandate.
WATCH | Parents, students react to school mask mandate
After a year and a half of COVID-related disruptions, there are many things Ariel Shorter, 17, is looking forward to going into her senior year at Gwendolyn Brooks College Prep. But wearing a mask while in class is not one of them.
"They have forced us to wear masks which puts us in an awkward situation. It makes us uncomfortable," Shorter said. "I actually told my principal if we had to wear masks I would rather stay at home because I'd rather be comfortable while learning."
Reaction to the governor's mask mandate has been swift and mixed. A former science teacher, Jurema Gorham, made the decision to homeschool her 9-year-old son last year. She's now moved him out of CPS and into Hyde Park's St. Thomas the Apostle Grade School. Chicago's Catholic Schools were not going to require masks for vaccinated students and staff, until now.
"I do believe it needs to be done, especially when you don't know where everyone coming into one space is coming from," Gorham said.
And while CPS had already announced that masks would be required in the fall, debate on both sides of the school masking issue has been raging in the suburbs. A meeting of Villa Park's School District 45 got contentious Tuesday night, with many of those in attendance refusing to wear masks.
"It's horrific our children that they are injuring their own children with having to wear a mask," attendee Bradley Donald said. "But even more horrific, you want to harm someone else's child to have them have a mask on."
A lobbyist for public school families statewide, Cassie Cresswell said she for one is glad the decision has been taken out of the hands of individual school districts.
"They are not epidemiologists, they are not immunologists. That's not an area of expertise you should expect your school administration to have," Cresswell said.
Both the Illinois Federation of Teachers and the Chicago Teachers Union today expressed their support for the governor's mandate.
COVID vaccine Chicago: Business lead charge in requiring masks, shots
It used to be "no shirt, no shoes, no service," but, with cases of COVID rising, some businesses are now saying "no shot, no service."
Metro Chicago, a concert hall in Wrigleyville, just announced that anyone attending shows there will be required to show proof of vaccination, unlike Lollapalooza, which allowed unvaccinated people to enter by providing a current negative COVID test.
Metro also said patrons will be required to show a government-issued photo ID, and it's recommended that everyone wear masks.
If you want to dine in restaurants and bars in NorthHalsted like D.S. Tequila Co. and Sidetrack, you better have proof of COVID vaccination, as it's now required to get in.
More and more restaurants and nightclubs around the Chicago area are making that move as COVID cases once again surge, driven by the spread of the delta variant, especially in unvaccinated populations.
RELATED: Some Chicago restaurants requiring masks, COVID vaccinations as cases increase
The move to require masks and ask for vaccination status is supported by Chicago Department of Public Health Commissioner Dr. Allison Arwady, even as she insisted the city has no plans yet to follow New York's move to mandate proof of vaccination for all indoor dining and fitness centers.
"I want to thank them for doing that. It is clearly one of the most important things they can do for reducing the risk for everybody in the restaurant," Arwady said.
The city is working on a way for people to digitally prove their vaccination status.
"We have a lot of people who lose their cards," Arwady explained. "We want people where there are settings that are wanting to either mandate vaccines or be checking vaccines as folks are coming in. I want to make that as technologically easy as possible in a way that protects everybody's privacy."
The Illinois Restaurant Association hopes individual restaurants will be allowed to make their own decisions, and pointed out that restaurants operating at high capacity or that are in neighborhoods with lower vaccination rates would be catastrophically affected by a vaccine mandate.
"We're still behind," said Sam Sanchez. "Every time you open the door and you're not operating at 100%, you're losing money."