The city isn't revealing how many people are there, but officials have said this is part of the site's preparation and training.
TIMELAPSE: Building of field hospital at Chicago's McCormick Place
Gov. JB Pritzker, Mayor Lori Lightfoot and Sen. Tammy Duckworth toured the facility Friday. They saw some of the more than 2,200 rooms.
The space will serve as primary care for patients with mild or moderate symptoms but also has isolation areas for patients whose conditions worsen.
"Where we're currently standing represents a new model of care for crises, what makes this place so unique is its ability to deliver care across a wide spectrum of medical severity," Dr. Christina Bratis said.
Officials have also placed a greater emphasis on testing to get Illinois to the point where it can reopen.
RELATED: Coronavirus Chicago: Mayor Lightfoot says city will wait to cancel summer events, tours McCormick Place alternate care facility
Tests have confirmed more than 25,000 positive COVID-19 cases in Illinois, but doctors believe there could be thousands more infected, or already recovered.
Discovering who has already recovered will be the focus of antibody testing that state labs are working to expand.
WATCH: See inside Chicago COVID-19 hospital at McCormick Place
"We need to know who may be infected as soon as we can before they come into contact with many other people, especially the most vulnerable," Illinois Department of Public Health Director Dr. Ngozi Ezike said.
The state of Illinois has expanded the parameters of those eligible to get a test to include anyone who had COVID-like symptoms, even if that person has not been given a doctor's order.
Pritzker said access to more labs that process the tests have allowed for the expansion.