The state made the announcement Thursday after data released from the CDC showed the majority of counties across Illinois are experiencing substantial or high COVID-19 transmission.
State officials say they will continue to evaluate the need for additional mitigations.
"Vaccines work – but we cannot promise those protections for every single future variant if we allow this virus to spread and mutate unchecked in our communities," said Gov. JB Pritzker. "With all the misinformation out there, I encourage all eligible Illinoisans who haven’t been vaccinated yet to talk to their doctors to alleviate any of their fears."
According to data from the CDC, the Delta variant accounts for more than 80-percent of recent COVID-19 cases in Illinois.
Officials say the Delta variant spreads more easily than other variants. Additionally, there is new evidence that a small number of fully vaccinated people who may be infected with Delta can infect others.
"While the vaccines have been proven to be effective against the Delta variant at preventing severe illness, hospitalization, and death, with this new evidence of breakthrough spread, we are adding another layer of protection for State employees and the people we serve," said IDPH Director Dr. Ngozi Ezike.
Under new requirements, Illinois state employees must wear a face covering that covers their nose and mouth while in the workplace or performing work duties in indoor settings outside their residence.
Additionally, employees must maintain physical distancing of at least six feet from any other person while in a workplace or performing work duties outside of their residence.
"The safety and well-being of State employees and residents remains top priority for the State, and this decision supports our efforts to provide a safe environment for our workforce and the people we serve," said Janel L. Forde, Director, Illinois Department of Central Management Services (CMS).
Visitors over the age of 2 are also required to wear face coverings while inside state offices and facilities, unless they are unable to medically tolerate a face covering, officials said.
State facilities will continue to receive regular cleaning services as well.
For more information, visit the state’s coronavirus website at https://coronavirus.illinois.gov/.