Travelers from the following states are affected:
The order will remain in effect until further notice. The city said that individuals found in violation of the quarantine order are subject to fines of $100 to $500 per day, up to $7,000.
"We felt like we had to do something to protect the progress we made in Chicago," said Public Health Commissioner Dr. Allison Arwady.
"This is about educating people into compliance. We're not going to send teams out to fine people into compliance," Mayor Lori Lightfoot said Monday. "We are not going on planes and saying you have to do 14 days of quarantine, no."
As of Monday, nearly everyone coming into Chicago from one of those 15 states has been asked to self-quarantine for two weeks, hoping to avoid the same spike in COVID-19 cases that is currently affecting the southern and western United States.
"These states are places where there are more than 15 cases every day per 100,000 population; that means they're at levels twice what we're seeing in Chicago," Arwady explained. "They're at a level of an outbreak where we were when we were under shelter in place."
But, will travelers comply?
"I happen to be a registered nurse at an area hospital, so that's very important for myself and the patients I take care of," said David Lange, who was returning from Atlanta.
"I bought my tickets before this whole quarantine thing started and I couldn't get out of them," said Olivia Jensen, who arrived at O'Hare from California.
"I have to go to work, so it's impossible," said Pashence Jackson, who was coming from Florida.
Even before the city imposed its travel order, Chicagoan Berkley Cameron decided she would self-quarantine following several days of work-related travel at Baylor Hospital in Dallas.
"I took a lot of precautions when I was there. I just went to the hospital. I went to the hotel. I didn't go to restaurants or anything. I was taking all the precautions. I don't think I have anything," Cameron said. "It's just caring about others when I come home, my family, my friends. If something would happen, and I gave it to somebody I couldn't live with myself. That would be awful."
Cameron said the planes she was on were packed.
"Even though I wore the N95 mask and everything, I would just feel more comfortable not being around people when I came back. I think that's the right thing to do," she said.
The quarantine order does not apply to essential workers or those engaging in medical-related travel.
"Better safe than sorry," said Annie Severs.
Severs and Jeanne Johnson spoke to ABC 7 Chicago as they waited for a family member returning from Tennessee.
"If you are not sure, and you've been around anybody that has been exposed: self-quarantine, it's just that simple" Johnson said.
Severs' son, who she was waiting for, does plan to quarantine once he is home.
According to the Chicago Department of Public Health, the states designated in the travel order have a significant degree of community-wide spread of COVID-19. A state will be designated if it has a case rate greater than 15 new COVID-19 cases per 100,000 resident population, per day, over a 7-day rolling average.
There are exceptions to the order, including essential work and medical travel.
Essential workers who must travel to Chicago must provide a certified note from their employer so that it can be reviewed by the health department and Chicago police. Essential workers will be subject to requirements that include limiting their activities to work-related activities and avoiding public spaces as much as possible.
Non-essential business travelers are also required to comply. Exceptions to the order for personal travel will be permitted for medical care and parental shared custody.
Back in May, Chicago health officials reported more than 1,000 cases and 50 deaths per day. Now the city is seeing well under 200 cases and about eight deaths per day.
If family and friends are coming to visit, family members who did not travel from a designated state are not required to self-quarantine.
"If people are coming to visit you from Chicago, you really want to make them aware of this," said Clint Henderson, a travel expert and senior news editor for The Points Guy. "The airlines and hotels have been very flexible in the age of coronavirus, so have them call their airline, have them call their hotel and ask them what their policies are. Most of the time they are able to get their money back if they have to cancel their trip."
The order will be revised every two weeks as conditions in the listed states evolve.
You can read the full emergency travel order and find frequently asked questions about the order on the Chicago Department of Public Health website.